[niepce] flatpak: use the latest gtkmm

[Hubert Figuière <hub src gnome org>]

commit 121981fa5ff486d1e80933df07f78a95950fdd31
Author: Hubert Figuière <hub figuiere net>
Date:   Mon Dec 31 15:42:45 2018 -0500

    flatpak: use the latest gtkmm

 flatpak/org.gnome.Niepce.json | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/flatpak/org.gnome.Niepce.json b/flatpak/org.gnome.Niepce.json
index dc7320c..6c16b78 100644
--- a/flatpak/org.gnome.Niepce.json
+++ b/flatpak/org.gnome.Niepce.json
@@ -234,8 +234,8 @@
             "sources" : [
                 {
                     "type" : "archive",
-                    "url" : "http://ftp.gnome.org/pub/GNOME/sources/gtkmm/3.22/gtkmm-3.22.2.tar.xz";,
-                    "sha256" : "91afd98a31519536f5f397c2d79696e3d53143b80b75778521ca7b48cb280090"
+                    "url" : "http://ftp.gnome.org/pub/GNOME/sources/gtkmm/3.24/gtkmm-3.24.0.tar.xz";,
+                    "sha256" : "cf5fc92805e581c8303e08d54519457ba07f15b766e9b1edde4862993ac1aa43"
                 }
             ]
         },