Add TruffleRuby 19.3.1

* See https://github.com/eregon/ruby-build/pull/1#issuecomment-573237440

README.md

@@ -13,7 +13,7 @@ This action currently supports these versions of MRI, JRuby and TruffleRuby:
 | ----------- | -------- |
 | Ruby | 2.3.0 - 2.3.8, 2.4.0 - 2.4.9, 2.5.0 - 2.5.7, 2.6.0 - 2.6.5, 2.7.0 |
 | JRuby | 9.2.9.0 |
-| TruffleRuby  | 19.3.0 |
+| TruffleRuby  | 19.3.0, 19.3.1 |
 
 The recommended way to refer to these versions is:
 `2.3`, `2.4`, `2.5`, `2.6`, `2.7`, `jruby`, `truffleruby`.  
@@ -24,6 +24,7 @@ for the always up-to-date list of available Ruby versions.
 
 Note that Ruby 2.3 and the OpenSSL version it needs (1.0.2) are both end-of-life,
 which means Ruby 2.3 is unmaintained and considered insecure.
+On Windows, Ruby 2.4 uses OpenSSL 1.0.2, which is no longer maintained.
 
 ### Supported Platforms
 
@@ -92,7 +93,27 @@ Otherwise (Ruby < 2.6), Bundler 1 is installed when that Ruby was built.
 
 ### Caching `bundle install`
 
-See this [example](https://github.com/actions/cache/blob/master/examples.md#ruby---gem) using [actions/cache](https://github.com/actions/cache).
+You can cache the installed gems with these two steps:
+
+```yaml
+    - uses: actions/cache@v1
+      with:
+        path: vendor/bundle
+        key: bundle-use-ruby-${{ matrix.os }}-${{ matrix.ruby }}-${{ hashFiles('**/Gemfile.lock') }}
+        restore-keys: |
+          bundle-use-ruby-${{ matrix.os }}-${{ matrix.ruby }}-
+    - name: Bundle install
+      run: |
+        bundle config path vendor/bundle
+        bundle install --jobs 4 --retry 3
+```
+
+When using a single job with a Ruby version, replace `${{ matrix.ruby }}` with the Ruby version.  
+When using `.ruby-version`, replace `${{ matrix.ruby }}` with `${{ hashFiles('.ruby-version') }}`.
+
+This uses the [cache action](https://github.com/actions/cache).
+The code above is a more complete version of the [Ruby - Gem example](https://github.com/actions/cache/blob/master/examples.md#ruby---gem).
+Make sure to include `use-ruby` in the `key` to avoid conflicting with previous caches.
 
 ## Limitations
 

dist/index.js

@@ -1399,6 +1399,10 @@ async function run() {
     if (platform === 'windows-latest') {
       rubyPrefix = await windows.downloadExtractAndSetPATH(ruby)
     } else {
+      if (ruby.startsWith('jruby')) {
+        // Workaround for https://github.com/actions/virtual-environments/issues/242
+        core.exportVariable('CLASSPATH', '')
+      }
       rubyPrefix = await downloadAndExtract(platform, ruby)
       core.addPath(`${rubyPrefix}/bin`)
     }

index.js

@@ -18,6 +18,10 @@ async function run() {
     if (platform === 'windows-latest') {
       rubyPrefix = await windows.downloadExtractAndSetPATH(ruby)
     } else {
+      if (ruby.startsWith('jruby')) {
+        // Workaround for https://github.com/actions/virtual-environments/issues/242
+        core.exportVariable('CLASSPATH', '')
+      }
       rubyPrefix = await downloadAndExtract(platform, ruby)
       core.addPath(`${rubyPrefix}/bin`)
     }