Update .gitlab-ci.yml
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index f627725..d45464f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -37,5 +37,9 @@
 build_test_job:
     stage: test
     environment: staging
+    only:
+      refs:
+      - master
+
     script:
     - "export DISPLAY=:0.0; cd org.polarsys.chess.parent; mvn $MAVEN_CLI_OPTS -P Neon-Java8,DevelopmentUpdateSite clean install"