[gnome-shell] build: Bump GTK+ requirement

[Florian Müllner <fmuellner src gnome org>]

commit 926f76635ee11a501fc2ba72c29218aa05b1fd82
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Oct 30 14:27:50 2014 +0000

    build: Bump GTK+ requirement
    
    GTK_POLICY_EXTERNAL requires at least 3.15.0

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 3a9e3ff..d55848b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -77,7 +77,7 @@ CLUTTER_MIN_VERSION=1.15.90
 GOBJECT_INTROSPECTION_MIN_VERSION=0.10.1
 GJS_MIN_VERSION=1.39.0
 MUTTER_MIN_VERSION=3.15.1
-GTK_MIN_VERSION=3.13.2
+GTK_MIN_VERSION=3.15.0
 GIO_MIN_VERSION=2.37.0
 LIBECAL_MIN_VERSION=3.5.3
 LIBEDATASERVER_MIN_VERSION=3.5.3