[gnome-font-viewer] flatpak: use current commit by default

[Cosimo Cecchi <cosimoc src gnome org>]

commit 2540e7eeeb1c4316486fdd65ab5f353a25aae9c6
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Mon Sep 3 17:14:40 2018 -0700

    flatpak: use current commit by default
    
    Since this is intended for testing.

 flatpak/org.gnome.font-viewer.json | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/flatpak/org.gnome.font-viewer.json b/flatpak/org.gnome.font-viewer.json
index 8949197..4716c64 100644
--- a/flatpak/org.gnome.font-viewer.json
+++ b/flatpak/org.gnome.font-viewer.json
@@ -38,7 +38,8 @@
             "sources": [
                 {
                     "type": "git",
-                    "path": ".."
+                    "path": "..",
+                    "branch": "HEAD"
                }
             ]
         }