[glade] CONTRIBUTING.md: Replace broken git clone URL with GNOME Gitlab URL

[Andre Klapper <aklapper src gnome org>]

commit 6d4e2cd7b77da8e2aa9a56b996c6402d1fd85bdc
Author: Andre Klapper <a9016009 gmx de>
Date:   Sun May 24 19:49:14 2020 +0200

    CONTRIBUTING.md: Replace broken git clone URL with GNOME Gitlab URL

 CONTRIBUTING.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index ff455474..732e4b32 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -18,10 +18,10 @@ Glade bugs are tracked at
 
 GIT
 ~~~
-You can browse the source code at https://git.gnome.org/browse/glade
+You can browse the source code at https://gitlab.gnome.org/GNOME/glade
 To check out a copy of Glade you can use the following command:
 
-       git clone git://git.gnome.org/glade
+       git clone https://gitlab.gnome.org/GNOME/glade.git
 
 Patches
 ~~~~~~~