Preparing for 0.2.1 release.
Preparing for 0.2.1 release.

ajmarquez/slack-ruby-client,jlyonsmith/slack-ruby-client,dblock/slack-ruby-client,mikz/slack-ruby-client,ajmarquez/slack-ruby-client,mikz/slack-ruby-client,dblock/slack-ruby-client,jlyonsmith/slack-ruby-client,slack-ruby/slack-ruby-client,slack-ruby/slack-ruby-client,jakedahn/slack-ruby-client,rkadyb/slack-ruby-client,jakedahn/slack-ruby-client,rkadyb/slack-ruby-client