Prevent private Gem being pushed to RubyGems (Bundler)

If you manage your gems using Bundler, you normally release the gem by the provided task:

rake release

More or less, this command do:

• Build the package
• Add a Git tag
• Push to RubyGems
  

This workflow is enough for most of cases, but if you're building a private gem, you probably want/need to skip last step. Bundler provides an ENV variable to achieve that with ease (add it at the top of your Rakefile):

ENV['gem_push']  = 'off'