[gnome-builder] flatpak: use 3.28 SDK for now

[Christian Hergert <chergert src gnome org>]

commit 9b7662fa27d042628bed5b4adc9633671fb6e43f
Author: Christian Hergert <chergert redhat com>
Date:   Tue May 22 11:46:23 2018 -0700

    flatpak: use 3.28 SDK for now
    
    The 3.30 SDK is going through a number of changes right now that make it
    unsuitable for our nightlies (including massive size increases). So lets
    just use the 3.28 SDK for now and pin our OSTree requirement so that we
    don't need to tweak gpgme stuff.

 build-aux/flatpak/org.gnome.Builder.json | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/build-aux/flatpak/org.gnome.Builder.json b/build-aux/flatpak/org.gnome.Builder.json
index d392a9c10..5c453792f 100644
--- a/build-aux/flatpak/org.gnome.Builder.json
+++ b/build-aux/flatpak/org.gnome.Builder.json
@@ -1,7 +1,7 @@
 {
     "app-id" : "org.gnome.Builder",
     "runtime" : "org.gnome.Sdk",
-    "runtime-version" : "master",
+    "runtime-version" : "3.28",
     "sdk" : "org.gnome.Sdk",
     "command" : "gnome-builder",
     "tags" : [
@@ -714,7 +714,8 @@
             "sources" : [
                 {
                     "type" : "git",
-                    "url" : "https://github.com/ostreedev/ostree.git";
+                    "url" : "https://github.com/ostreedev/ostree.git";,
+                    "tag" : "v2018.5"
                 }
             ]
         },