[gnome-builder] build: add --device=dri for flatpak

[Christian Hergert <chergert src gnome org>]

commit c4d5fbeb0863ce12bcd0f0c09343a2e5bcb5f9be
Author: Christian Hergert <chergert redhat com>
Date:   Tue Mar 12 10:17:58 2019 -0700

    build: add --device=dri for flatpak
    
    This allows OpenGL access so that WebKit can create a nested compositor.

 build-aux/flatpak/org.gnome.Builder.json | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/build-aux/flatpak/org.gnome.Builder.json b/build-aux/flatpak/org.gnome.Builder.json
index 7ad16b121..3e1709ff9 100644
--- a/build-aux/flatpak/org.gnome.Builder.json
+++ b/build-aux/flatpak/org.gnome.Builder.json
@@ -12,6 +12,7 @@
         "--require-version=1.0.0",
         "--allow=devel",
         "--talk-name=org.freedesktop.Flatpak",
+        "--device=dri",
         "--share=ipc",
         "--socket=x11",
         "--socket=wayland",