chore: disable npm install on Travis

Grunt is configured to run `npm install` before every task. That is convenient when switching a branch for example.

On Travis, this makes no sense and is causing tons of NPM warnings (eg. packages not defining repository field etc).

Author: vojtajina

lib/grunt/utils.js

@@ -7,7 +7,9 @@ var version;
 module.exports = {
 
   init: function() {
-    shell.exec('npm install');
+    if (!process.env.TRAVIS) {
+      shell.exec('npm install');
+    }
   },