Cache bundle gems not working

[jeffreytse]

Since getting OS name from /etc/os-release and saving to the bundle's folder is always failed, this causes caching bundle gems not working.

[jeffreytse]

We can use a CACHE_VERSION secrect for better updating the cache as below code snippet.

# Use GitHub Actions' cache to cache dependencies on servers
- uses: actions/cache@v2
  with:
    path: vendor/bundle
    key: ${{ runner.os }}-gems-${{ secrets.CACHE_VERSION }}-${{ hashFiles('**/Gemfile.lock') }}
    restore-keys: |
      ${{ runner.os }}-gems-