[gnome-sdk-images] Pin vala to 0.36

[Matthias Clasen <matthiasc src gnome org>]

commit f4842204e43bf24de1e8ee00ede10178eea48a04
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jul 5 13:52:28 2017 -0400

    Pin vala to 0.36
    
    master has a hard dependency on graphviz that breaks the sdk
    build.

 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 27bc736..ed5f308 100644
--- a/org.gnome.Sdk.json.in
+++ b/org.gnome.Sdk.json.in
@@ -168,7 +168,8 @@
             "sources": [
                 {
                     "type": "git",
-                    "url": "git://git.gnome.org/vala"
+                    "url": "git://git.gnome.org/vala",
+                    "branch": "0.36"
                 }
             ]
         },