Fix Bundler warning and Bump version to 0.2.2

original warning messages:

mixable_engines at ~/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/bundler/gems/mixable_engines-42ef43258196 did not have a valid gemspec.
This prevents bundler from installing bins or native extensions, but that may not affect its functionality.
The validation message from Rubygems was:
  ["README.rdoc"] are not files