### What changes were proposed in this pull request?
This PR makes it do not change R version when releasing preview versions.

### Why are the changes needed?
Failed to make Spark binary distribution:
```
++ . /opt/spark-rm/output/spark-3.0.0-preview2-bin-hadoop2.7/R/find-r.sh
+++ '[' -z /usr/bin ']'
++ /usr/bin/Rscript -e ' if("devtools" %in% rownames(installed.packages())) { library(devtools); devtools::document(pkg="./pkg", roclets=c("rd")) }'
Loading required package: usethis
Updating SparkR documentation
First time using roxygen2. Upgrading automatically...
Loading SparkR
Invalid DESCRIPTION:
Malformed package version.

See section 'The DESCRIPTION file' in the 'Writing R Extensions'
manual.

Error: invalid version specification '3.0.0-preview2'
In addition: Warning message:
roxygen2 requires Encoding: UTF-8
Execution halted
[ERROR] Command execution failed.
org.apache.commons.exec.ExecuteException: Process exited with an error: 1 (Exit value: 1)
    at org.apache.commons.exec.DefaultExecutor.executeInternal (DefaultExecutor.java:404)
    at org.apache.commons.exec.DefaultExecutor.execute (DefaultExecutor.java:166)
    at org.codehaus.mojo.exec.ExecMojo.executeCommandLine (ExecMojo.java:804)
    at org.codehaus.mojo.exec.ExecMojo.executeCommandLine (ExecMojo.java:751)
    at org.codehaus.mojo.exec.ExecMojo.execute (ExecMojo.java:313)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:498)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary for Spark Project Parent POM 3.0.0-preview2:
[INFO]
[INFO] Spark Project Parent POM ........................... SUCCESS [ 18.619 s]
[INFO] Spark Project Tags ................................. SUCCESS [ 13.652 s]
[INFO] Spark Project Sketch ............................... SUCCESS [  5.673 s]
[INFO] Spark Project Local DB ............................. SUCCESS [  2.081 s]
[INFO] Spark Project Networking ........................... SUCCESS [  3.509 s]
[INFO] Spark Project Shuffle Streaming Service ............ SUCCESS [  0.993 s]
[INFO] Spark Project Unsafe ............................... SUCCESS [  7.556 s]
[INFO] Spark Project Launcher ............................. SUCCESS [  5.522 s]
[INFO] Spark Project Core ................................. FAILURE [01:06 min]
[INFO] Spark Project ML Local Library ..................... SKIPPED
[INFO] Spark Project GraphX ............................... SKIPPED
[INFO] Spark Project Streaming ............................ SKIPPED
[INFO] Spark Project Catalyst ............................. SKIPPED
[INFO] Spark Project SQL .................................. SKIPPED
[INFO] Spark Project ML Library ........................... SKIPPED
[INFO] Spark Project Tools ................................ SKIPPED
[INFO] Spark Project Hive ................................. SKIPPED
[INFO] Spark Project Graph API ............................ SKIPPED
[INFO] Spark Project Cypher ............................... SKIPPED
[INFO] Spark Project Graph ................................ SKIPPED
[INFO] Spark Project REPL ................................. SKIPPED
[INFO] Spark Project Assembly ............................. SKIPPED
[INFO] Kafka 0.10+ Token Provider for Streaming ........... SKIPPED
[INFO] Spark Integration for Kafka 0.10 ................... SKIPPED
[INFO] Kafka 0.10+ Source for Structured Streaming ........ SKIPPED
[INFO] Spark Project Examples ............................. SKIPPED
[INFO] Spark Integration for Kafka 0.10 Assembly .......... SKIPPED
[INFO] Spark Avro ......................................... SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  02:04 min
[INFO] Finished at: 2019-12-16T08:02:45Z
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.6.0:exec (sparkr-pkg) on project spark-core_2.12: Command execution failed.: Process exited with an error: 1 (Exit value: 1) -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
[ERROR]
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <args> -rf :spark-core_2.12
```

### Does this PR introduce any user-facing change?
No.

### How was this patch tested?
manual test:
```diff
diff --git a/R/pkg/R/sparkR.R b/R/pkg/R/sparkR.R
index cdb59093781..b648c51e010 100644
--- a/R/pkg/R/sparkR.R
+++ b/R/pkg/R/sparkR.R
 -336,8 +336,8  sparkR.session <- function(

   # Check if version number of SparkSession matches version number of SparkR package
   jvmVersion <- callJMethod(sparkSession, "version")
-  # Remove -SNAPSHOT from jvm versions
-  jvmVersionStrip <- gsub("-SNAPSHOT", "", jvmVersion)
+  # Remove -preview2 from jvm versions
+  jvmVersionStrip <- gsub("-preview2", "", jvmVersion)
   rPackageVersion <- paste0(packageVersion("SparkR"))

   if (jvmVersionStrip != rPackageVersion) {

```

Closes #26904 from wangyum/SPARK-30265.

Authored-by: Yuming Wang <yumwang@ebay.com>
Signed-off-by: Yuming Wang <wgyumg@gmail.com>