[gnome-sdk-images] Build gtk3 from the gtk-3-22 branch

[Matthias Clasen <matthiasc src gnome org>]

commit c6790b8ec3dcc42cddcfb2ed073ba509caebc5ce
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Oct 7 07:36:52 2016 -0400

    Build gtk3 from the gtk-3-22 branch

 org.gnome.Sdk.json.in |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/org.gnome.Sdk.json.in b/org.gnome.Sdk.json.in
index fe41b58..640b3eb 100644
--- a/org.gnome.Sdk.json.in
+++ b/org.gnome.Sdk.json.in
@@ -345,7 +345,8 @@
             "sources": [
                 {
                     "type": "git",
-                    "url": "git://git.gnome.org/gtk+"
+                    "url": "git://git.gnome.org/gtk+",
+                    "branch": "gtk-3-22"
                 }
             ]
         },