Try showing eslint output with log file

.gitlab-ci.yml

@@ -35,7 +35,8 @@ eslint:
   script:
     - npm install
     # eslint exits 0 on warnings, this is a workaround to exit 1 when warnings are present.
-    - '! npm run lint | tee "$(tty)" | grep -qE ''✖ [0-9]+ problem'''
+    - '! npm run lint | tee lint.log'
+    - "grep -qE '✖ [0-9]+ problem' lint.log"
   allow_failure: true
   needs: []