[SPARKR][MINOR] Fix Cache Folder Path in Windows

## What changes were proposed in this pull request?

This PR tries to fix the scheme of local cache folder in Windows. The name of the environment variable should be `LOCALAPPDATA` rather than `%LOCALAPPDATA%`.

## How was this patch tested?

Manual test in Windows 7.

Author: Junyang Qian <junyangq@databricks.com>

Closes #14743 from junyangq/SPARKR-FixWindowsInstall.

R/pkg/R/install.R

@@ -212,7 +212,7 @@ hadoop_version_name <- function(hadoopVersion) {
 # adapt to Spark context
 spark_cache_path <- function() {
   if (.Platform$OS.type == "windows") {
-    winAppPath <- Sys.getenv("%LOCALAPPDATA%", unset = NA)
+    winAppPath <- Sys.getenv("LOCALAPPDATA", unset = NA)
     if (is.na(winAppPath)) {
       msg <- paste("%LOCALAPPDATA% not found.",
                    "Please define the environment variable",