[gnome-boxes] ci: Build against Fedora Rawhide

[Felipe Borges <felipeborges src gnome org>]

commit b6a066700597ca503d576890f70f5aa0ec56cc6b
Author: Felipe Borges <felipeborges gnome org>
Date:   Thu Apr 5 15:11:35 2018 +0200

    ci: Build against Fedora Rawhide
    
    Rawhide guarantees we will have the latest versions of our deps.

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a1a27cd9..9a18d6e9 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,4 +1,4 @@
-image: fedora:27
+image: fedora:rawhide
 
 before_script:
     - dnf install -y meson vala gtk3-devel libgovirt-devel