Flatpak: Switch to stable branch

flatpak/org.gajim.Gajim.yaml

@@ -3,8 +3,6 @@ runtime: org.gnome.Platform
 runtime-version: 3.30
 sdk: org.gnome.Sdk
 command: gajim
-tags: nightly
-desktop-file-name-prefix: '(Nightly) '
 finish-args:
   - --share=ipc
   - --share=network
@@ -193,5 +191,6 @@ modules:
     sources:
       - type: git
         url: https://dev.gajim.org/gajim/gajim.git
+        branch: gajim_1.1
     post-install:
       - install -d /app/plugins