travis: add grunt as global

Author: dimaspirit

package.json

@@ -74,7 +74,7 @@
     }
   },
   "scripts": {
-    "build": "npm i && npm install -g jasmine && grunt",
+    "build": "npm install -g jasmine && npm install -g grunt && grunt",
     "test": "jasmine"
   }
 }