build: require GTK+ 3.13.2

For new RTL icons handling.

https://bugzilla.gnome.org/show_bug.cgi?id=736079
evince-viewer: Fix the icons in RTL

With newer GTK+ the custom handling for RTL
icons are wrong.

https://bugzilla.gnome.org/show_bug.cgi?id=736079
audio: Fix the icons in RTL

With newer GTK+ the custom handling for RTL
icons are wrong.

https://bugzilla.gnome.org/show_bug.cgi?id=736079
gst: Fix the icons in RTL

With newer GTK+ the custom handling for RTL
icons are wrong.

https://bugzilla.gnome.org/show_bug.cgi?id=736079