[gimp/wip/schumaml/gitlab-ci] build: .gitlab-ci.yml: add xorg-server-xvfb for make check

[Michael Schumacher <schumaml src gnome org>]

commit 234ec680a60d94cf829916cdd387e55cd254cd79
Author: Michael Schumacher <schumaml gmx de>
Date:   Sun Jul 21 16:39:54 2019 +0200

    build: .gitlab-ci.yml: add xorg-server-xvfb for make check

 .gitlab-ci.yml | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 6da0d67787..63e7b4b612 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -153,6 +153,7 @@ gegl-git-autotools:
         gtk-doc
         intltool
         iso-codes
+        xorg-server-xvfb
     - git clone --depth=$GIT_DEPTH https://gitlab.gnome.org/GNOME/gimp.git _gimp
     - cd _gimp
     - mkdir _build