Add cask for Qt Creator
user
```ruby
class QtCreator < Cask
  url 'http://download.qt-project.org/official_releases/qtcreator/2.8/2.8.1/qt-creator-mac-opensource-2.8.1.dmg'
  homepage 'http://qt-project.org/'
  version '2.8.1'
  sha1 '49033ed85f191ab8c6f191b74a47a7f945ce5c0b'
  link 'Qt Creator.app'
end
```
assistant