Update .gitlab-ci.yml file

.gitlab-ci.yml

@@ -27,7 +27,7 @@ test-job:        # This job runs in the test stage.
       if [ -z "$CI_COMMIT_SHA" ]; then 
         files=$(find . -name "*.zone" -printf %P)
       else
-        files=$(git diff-tree --no-commit-id --name-only -r $CI_COMMIT_SHA | grep zone)
+        files=$(echo $(git diff-tree --no-commit-id --name-only -r $CI_COMMIT_SHA) | grep zone)
       fi
     - |+
       if [ -z "$files" ]; then