[gnome-builder] flatpak: make vapi writable

[Christian Hergert <chergert src gnome org>]

commit 6d7a6f59f3336273b788886bc12a5ff0cfcb30e9
Author: Christian Hergert <chergert redhat com>
Date:   Fri Jan 3 17:13:10 2020 -0800

    flatpak: make vapi writable
    
    We really dont want this long term, but see if it makes things build.

 build-aux/flatpak/org.gnome.Builder.json | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/build-aux/flatpak/org.gnome.Builder.json b/build-aux/flatpak/org.gnome.Builder.json
index f2cead3ee..ce4ba92f4 100644
--- a/build-aux/flatpak/org.gnome.Builder.json
+++ b/build-aux/flatpak/org.gnome.Builder.json
@@ -593,6 +593,9 @@
             ],
             "buildsystem" : "meson",
             "builddir" : true,
+            "ensure-writable" : [
+                "/usr/share/vala/vapi"
+           ],
             "sources" : [
                 {
                     "type" : "git",