Update npm version on travis

Author: niklasvh

.travis.yml

@@ -8,6 +8,8 @@ node_js:
 - '4.1'
 before_script:
 - npm install
+before_install:
+  npm install -g npm@'>=2.13.5'
 deploy:
   - provider: npm
     email: niklasvh@gmail.com