[gnome-todo] flatpak: Build GTK4

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 2615f02e652c8875002bef29465b8f289777f355
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Thu Mar 28 17:31:36 2019 -0300

    flatpak: Build GTK4
    
    The GNOME Platform is going through many changes and is a
    bit unstable. Until dust has settled, build GTK4 ourselves.

 build-aux/flatpak/org.gnome.Todo.json | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
---
diff --git a/build-aux/flatpak/org.gnome.Todo.json b/build-aux/flatpak/org.gnome.Todo.json
index a08247e..b6b2b81 100644
--- a/build-aux/flatpak/org.gnome.Todo.json
+++ b/build-aux/flatpak/org.gnome.Todo.json
@@ -128,6 +128,25 @@
                 }
             ]
         },
+        {
+            "name" : "gtk4",
+            "buildsystem": "meson",
+            "builddir": true,
+            "config-opts": [
+                "-Dbuild-examples=false",
+                "-Dbuild-tests=false",
+                "-Ddemos=false",
+                "--prefix=/app",
+                "--libdir=/app/lib"
+            ],
+            "sources": [
+                {
+                    "type": "git",
+                    "url": "https://gitlab.gnome.org/GNOME/gtk.git";
+                }
+            ]
+
+        },
         {
             "name" : "flatpak-wrapper",
             "buildsystem" : "simple",