[gnome-todo] flatpak: Add libportal

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

commit dc5c285943451896b8643e663bb90e391832fc3e
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Fri Feb 21 18:32:03 2020 -0300

    flatpak: Add libportal

 build-aux/flatpak/org.gnome.Todo.json | 10 ++++++++++
 1 file changed, 10 insertions(+)
---
diff --git a/build-aux/flatpak/org.gnome.Todo.json b/build-aux/flatpak/org.gnome.Todo.json
index 0dca921..b19db31 100644
--- a/build-aux/flatpak/org.gnome.Todo.json
+++ b/build-aux/flatpak/org.gnome.Todo.json
@@ -147,6 +147,16 @@
                 }
             ]
         },
+        {
+            "name" : "libportal",
+            "buildsystem" : "meson",
+            "sources" : [
+                {
+                    "type" : "git",
+                    "url" : "https://github.com/flatpak/libportal.git";
+                }
+            ]
+        },
         {
             "name" : "gnome-todo",
             "buildsystem" : "meson",