Update .gitlab-ci.yml file

.gitlab-ci.yml

@@ -23,7 +23,7 @@ stages:          # List of stages for jobs, and their order of execution
 
 build-job:
        # This job runs in the build stage, which runs first.
-  run-on: ubuntu-latest
+  runs-on: ubuntu-latest
   stage: build
   script:
     - echo "Compiling the code..."