[gnome-builder] CI: Use the master gnome-sdk runtime

[Jordan Petridis <jpetridis src gnome org>]

commit 1562b612eb577ef6222def7cabddb3a0ba30481c
Author: Jordan Petridis <jordanpetridis protonmail com>
Date:   Tue Aug 7 22:35:35 2018 +0000

    CI: Use the master gnome-sdk runtime
    
    Followup of cc3b47406f2248fbc6ede65e70fe9e23217756d6

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 040378765..dbe29934f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -6,7 +6,7 @@ variables:
     BUNDLE: "gnome-builder-git.flatpak"
 
 flatpak:
-    image: "registry.gitlab.gnome.org/gnome/gnome-runtime-images/gnome:3.28"
+    image: "registry.gitlab.gnome.org/gnome/gnome-runtime-images/gnome:master"
     stage: test
     variables:
         GIT_SUBMODULE_STRATEGY: normal