Fixed AboutDialog

On phones with Android 2.3 "OK" button in *AboutDialog* wasn't displayed properly. I fixed this issue.

Screenshots: [before](http://i.imgur.com/cDq2tE6.png) and [after](http://i.imgur.com/3NhxWz1.png).

Also, button looks [a bit better](http://i.imgur.com/Re1Us86.png) now on newer devices.