[gnome-usage] gitlab-ci: Update for Fedora 28 and fix failing CI pipelines

[Felipe Borges <felipeborges src gnome org>]

commit ee73691f504e3e900a54613af2ba10be7d7bbae0
Author: carpediem <reachadityahere+gitlab gmail com>
Date:   Thu Jun 7 23:09:55 2018 +0200

    gitlab-ci: Update for Fedora 28 and fix failing CI pipelines

 .gitlab-ci.yml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 05ed1b9..fcdb9e2 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,7 +1,8 @@
-image: fedora:26
+image: fedora:28
 stages:
   - build
 before_script:
+  - dnf update -y
   - dnf install -y gcc meson gettext gtk-doc vala gtk3-devel libgtop2-devel
                    desktop-file-utils
 build-gnome-usage: