Merge branch 'upgrade-dockerfile' into 'master'

Upgrade Docker build to GitLab v7.8.3

Upgrading from GitLab v7.8.1. Pretty simple change, tested with a quick Docker build.

See merge request !380

docker/Dockerfile

@@ -11,7 +11,7 @@ RUN apt-get update -q \
 # If the Omnibus package version below is outdated please contribute a merge request to update it.
 # If you run GitLab Enterprise Edition point it to a location where you have downloaded it.
 RUN TMP_FILE=$(mktemp); \
-    wget -q -O $TMP_FILE https://downloads-packages.s3.amazonaws.com/ubuntu-14.04/gitlab_7.8.1-omnibus-1_amd64.deb \
+    wget -q -O $TMP_FILE https://downloads-packages.s3.amazonaws.com/ubuntu-14.04/gitlab_7.8.3-omnibus-1_amd64.deb \
     && dpkg -i $TMP_FILE \
     && rm -f $TMP_FILE