Documentation fix.

Hey Steve, the gem is pretty hard to find as it's named almost identically to `gem afterparty`, so I was looking into gem's sources while trying to use it. The doc appeared to be outdated.

Then I remembered that someone told me "if you have any questions with after_part you should ask Steve", which brought me an idea of that the gem is yours. You are way more easier to be found on github than the gem, so I found your profile and you know the after party.