Added CodeClimate badge. [ci skip]
Added CodeClimate badge. [ci skip]

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