Build-depend on gir1.2-gtk-3.0

This is because Ubuntu 14.10's libgjs0e package doesn't have a runtime
dependency on it. However, in order to import GjsPrivate-1.0.typelib, you
need it. This causes a build failure on Ubuntu 14.10.

debian/control

@@ -5,6 +5,7 @@ Maintainer: Philip Chimento <[email protected]>
 Build-Depends: autotools-dev,
                debhelper (>= 9),
                gir1.2-glib-2.0,
+               gir1.2-gtk-3.0,
                gjs (>= 1.39.3)
 Standards-Version: 3.9.5
 Homepage: https://github.com/ptomato/jasmine-gjs