[pitivi] build: Fix devenv building gst-devtools

[Alexandru Băluț <alexbalut src gnome org>]

commit fc84d0e6eb0f78a92bc9b4eddd12760df082f8d4
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Sat Mar 23 22:56:05 2019 +0100

    build: Fix devenv building gst-devtools
    
    gst-devtools wants to install the Debug Viewer in a read-only place.

 build/flatpak/org.pitivi.Pitivi.json | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/build/flatpak/org.pitivi.Pitivi.json b/build/flatpak/org.pitivi.Pitivi.json
index d1117f81..ed72f75f 100644
--- a/build/flatpak/org.pitivi.Pitivi.json
+++ b/build/flatpak/org.pitivi.Pitivi.json
@@ -587,6 +587,7 @@
             "builddir": true,
             "config-opts": [
                 "-Dgtk_doc=disabled",
+                "-Ddebug_viewer=false",
                 "--libdir=lib"
             ],
             "sources": [