[MINOR] Bump R version to 2.2.0.

## What changes were proposed in this pull request?
#16126 bumps master branch version to 2.2.0-SNAPSHOT, but it seems R version was omitted.

## How was this patch tested?
N/A

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #16488 from yanboliang/r-version.

R/pkg/DESCRIPTION

 Package: SparkR
 Type: Package
-Version: 2.1.0
+Version: 2.2.0
 Title: R Frontend for Apache Spark
 Description: The SparkR package provides an R Frontend for Apache Spark.
 Authors@R: c(person("Shivaram", "Venkataraman", role = c("aut", "cre"),