Get the cache for testing.

* master:
  Enable caching for specs and remove configurable git cache size.
  Save Git chaches in ~/Library/Caches/CocoaPods/Git.
  [Downloader::Git] Skip cache pull if ref is available.
  Restored Pod::Downloader::Git::GitHub.
  [Git] Fix for Travis errors.
  [Git] Increased default cache to 500Mb.
  [Downloader::Git] Completed cache support
  [Git<<Downloader] Fix for url hash
  [Downloader::Git] Cache repos