add npm install in travis after success

Author: Anthony Sendra

.travis.yml

@@ -13,6 +13,7 @@ after_success:
   - git config --global user.name "Travis CI"
   - git clone --quiet --branch=${TRAVIS_BRANCH} https://${GH_TOKEN}@github.com/${TRAVIS_REPO_SLUG} travis-build
   - cd travis-build
+  - npm install
   - grunt
   - git add dist/
   - git commit -am "Travis CI - [ci skip] - automatic dist folder"