Try with npm 2...

redox · redox · commit b90efc819537 · 2016-04-08T21:40:36.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -29,6 +29,7 @@ env:
 node_js:
 - 5
 before_script:
+- npm install -g npm@~2
 - npm install -g grunt-cli
 - npm install -g node-static
 - grunt build
