Build npm package when tag present only

Author: miaulightouch

.travis.yml

@@ -28,6 +28,7 @@ jobs:
         - cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js
         - rm -rf ./coverage
     - stage: npm release
+      if: tag IS present
       node_js: "8"
       script: 
         - yarn build