No longer remove the prefix before extraction, extracting should be idempotent

* Fixes #191

Author: eregon

dist/index.js

@@ -50,7 +50,7 @@ export async function install(platform, engine, version) {
   common.setupPath([path.join(rubyPrefix, 'bin')])
 
   if (!inToolCache) {
-    await preparePrefix(rubyPrefix)
+    await io.mkdirP(rubyPrefix)
     if (engine === 'truffleruby+graalvm') {
       await installWithRubyBuild(engine, version, rubyPrefix)
     } else {
@@ -61,15 +61,6 @@ export async function install(platform, engine, version) {
   return rubyPrefix
 }
 
-async function preparePrefix(rubyPrefix) {
-  const parentDir = path.dirname(rubyPrefix)
-
-  await io.rmRF(rubyPrefix)
-  if (!(fs.existsSync(parentDir) && fs.statSync(parentDir).isDirectory())) {
-    await io.mkdirP(parentDir)
-  }
-}
-
 async function installWithRubyBuild(engine, version, rubyPrefix) {
   const tmp = process.env['RUNNER_TEMP'] || os.tmpdir()
   const rubyBuildDir = path.join(tmp, 'ruby-build-for-setup-ruby')