[GTK] Missing atk in install-dependencies script
https://bugs.webkit.org/show_bug.cgi?id=112272

Reviewed by Gustavo Noronha Silva.

* gtk/install-dependencies: Add missing atk dependency.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146472 268f45cc-cd09-0410-ab3c-d52691b4dbfc