chore(travis): install grunt before tests

Author: Alexandre-io

.travis.yml

@@ -5,5 +5,6 @@ node_js:
   - '3'
   - '2'
   - '0.12'
-sudo: false
-script: npm install . && grunt test
+before_script:
+  - npm install grunt-cli -g
+script: npm install . && npm test

package.json

@@ -4,7 +4,7 @@
   "description": "Introductions for websites to guide step-by-step your users.",
   "main": ["src/introduction.js", "introduction.angular.js"],
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "grunt test"
   },
   "repository": {
     "type": "git",