Revert "remove tag from runner to test on gitlab.com"

This reverts commit 6043d2ef

.gitlab-ci.yml

@@ -8,6 +8,8 @@ stages:
 test:
   stage: test
   image: openjdk:8
+  tags:
+    - mbr
   script:
     - ./gradlew --no-daemon test --fail-fast --tests "org.memobase.Tests"