Bug 1356123 - Add missing locales package to the lint docker image. r=gps

For some reason, the locales package is not installed anymore during the
docker image build, which leads to the locale-gen command failing, since
it's not there.

--HG--
extra : rebase_source : 0a152499c623a00d27d8b916c472e5d5980d8193

taskcluster/docker/lint/system-setup.sh

@@ -11,6 +11,7 @@ cd /setup
 
 apt_packages=()
 apt_packages+=('curl')
+apt_packages+=('locales')
 apt_packages+=('python')
 apt_packages+=('python-pip')
 apt_packages+=('sudo')