[gcr] .gitlab-ci.yml: Install diffutils

[Daiki Ueno <dueno src gnome org>]

commit 29f1845c6a65376d4084da1775383ce8505be257
Author: Daiki Ueno <dueno src gnome org>
Date:   Fri Nov 1 17:30:44 2019 +0100

    .gitlab-ci.yml: Install diffutils
    
    The diff command is no longer pulled in by default in F31.
    Spotted by Petr Sumbera.

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 4893870..18825f0 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -3,7 +3,7 @@ stages:
   - deploy
 
 variables:
-  DEPENDENCIES: dbus-x11 gcc gtk-doc make openssh python redhat-rpm-config
+  DEPENDENCIES: dbus-x11 diffutils gcc gtk-doc make openssh python redhat-rpm-config
 
 fedora:Werror:
   image: fedora:latest