[gnome-calculator] ci: Add required apt-get update step

[Ken VanDine <kvandine src gnome org>]

commit 1079381e49a0280b2c77390f512dfc00dbff1740
Author: Ken VanDine <ken vandine org>
Date:   Tue Jun 11 11:36:19 2019 -0400

    ci: Add required apt-get update step

 .gitlab-ci.yml | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 36bc70c6..23d3d654 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -35,6 +35,8 @@ build:ubuntu:
 build:snap:
   stage: build
   image: ubuntudesktop/gnome-3-28-1804
+  before_script:
+    - apt-get update
   script: snapcraft
   allow_failure: true
   artifacts: