[gnome-apps-nightly] Fetch gitg manifest from it's own repo.

[Jordan Petridis <jpetridis src gnome org>]

commit 0284ebef66dad1d5dd74e3ed9c18cef6c0e88277
Author: Jordan Petridis <jordanpetridis protonmail com>
Date:   Mon Jul 23 00:42:51 2018 +0300

    Fetch gitg manifest from it's own repo.

 org.gnome.gitg.app  |   1 +
 org.gnome.gitg.json | 130 ----------------------------------------------------
 2 files changed, 1 insertion(+), 130 deletions(-)
---
diff --git a/org.gnome.gitg.app b/org.gnome.gitg.app
index 1fad11d..df6310d 100644
--- a/org.gnome.gitg.app
+++ b/org.gnome.gitg.app
@@ -1,2 +1,3 @@
 ID=org.gnome.gitg
 JSON=org.gnome.gitg.json
+GITURL=https://gitlab.gnome.org/GNOME/gitg.git