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

[Jeremy Bicha <jbicha src gnome org>]

commit c6dad1719d3dbcf77bf1489c565d0a33a9df8ae4
Author: Jeremy Bicha <jbicha ubuntu com>
Date:   Wed Jan 30 19:10:27 2019 -0500

    ci: Add required apt-get update step

 .gitlab-ci.yml | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 4ecbd503..4a423b8b 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -36,6 +36,7 @@ build:snap:
   stage: build
   image: snapcore/snapcraft
   before_script:
+    - apt-get update
     - apt-get install -q -y --no-install-recommends software-properties-common
     - add-apt-repository -yu ppa:ubuntu-desktop/gnome-3-26
   script: snapcraft