[gnome-nibbles] Fix flatpak build

[Iulian Radu <iulianradu src gnome org>]

commit f214d84ca60459129268be05dbe86ad6c845e1e9
Author: Iulian Gabriel RADU <gradu bitdefender com>
Date:   Fri Jan 3 14:30:19 2020 +0200

    Fix flatpak build
    
    libgnome-games-support is now using meson as a build system.

 org.gnome.Nibbles.json | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/org.gnome.Nibbles.json b/org.gnome.Nibbles.json
index 4f81b5f..a67fbfc 100644
--- a/org.gnome.Nibbles.json
+++ b/org.gnome.Nibbles.json
@@ -34,13 +34,14 @@
         },
         {
             "name": "libgnome-games-support",
+            "buildsystem": "meson",
             "sources": [
                 {
                     "type": "git",
                     "url": "https://gitlab.gnome.org/GNOME/libgnome-games-support.git";
                 }
             ]
-        },       
+        },
         {
             "name": "gnome-nibbles",
             "buildsystem": "meson",