Further improve settings for extra tests from GitLab

tests/gitlab.yml

@@ -26,7 +26,7 @@ Code Quality:
     REPORT_FORMAT: html
   script:
     - |
-      export SOURCE_CODE='$(php /usr/local/bin/volume.php /code) | cut -d: -f1
+      export SOURCE_CODE=$(php /usr/local/bin/volume.php /code) | cut -d: -f1
     - |
       if ! docker info &>/dev/null; then
         if [ -z "$DOCKER_HOST" -a "$KUBERNETES_PORT" ]; then