gtk+3: fix since glib-utils
gtk+3: fix since glib-utils

After the refactor of `glib` and `glib-utils` a number of formulas no
longer build. This fixes gtk+3.

chrisfinazzo/homebrew-core,lemzwerg/homebrew-core,zyedidia/homebrew-core,filcab/homebrew-core,sjackman/homebrew-core,chrisfinazzo/homebrew-core,makigumo/homebrew-core,zyedidia/homebrew-core,stgraber/homebrew-core,adam-moss/homebrew-core,lemzwerg/homebrew-core,Homebrew/homebrew-core,nandub/homebrew-core,nandub/homebrew-core,makigumo/homebrew-core,Homebrew/homebrew-core,filcab/homebrew-core,nbari/homebrew-core,stgraber/homebrew-core,adam-moss/homebrew-core,sjackman/homebrew-core,nbari/homebrew-core