[mutter] ci/Dockerfile: Pass --no-cache in build example

[Jonas Ådahl <jadahl src gnome org>]

commit 07de258f48d77086f23a85a5c86e0290371c38f8
Author: Jonas Ådahl <jadahl gmail com>
Date:   Wed Aug 14 11:34:56 2019 +0200

    ci/Dockerfile: Pass --no-cache in build example
    
    Using the cache means we don't get updates from Fedora or copr.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/726

 .gitlab-ci/Dockerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci/Dockerfile b/.gitlab-ci/Dockerfile
index 860430020..e98518ae8 100644
--- a/.gitlab-ci/Dockerfile
+++ b/.gitlab-ci/Dockerfile
@@ -1,7 +1,7 @@
 # Rebuild and push with
 #
 #     cd .gitlab-ci/
-#     docker build -t registry.gitlab.gnome.org/gnome/mutter/master:v2 .
+#     docker build --no-cache -t registry.gitlab.gnome.org/gnome/mutter/master:v2 .
 #     docker push registry.gitlab.gnome.org/gnome/mutter/master:v2
 #