Update package.json to work with node v6.x

README.md

@@ -4,6 +4,7 @@
 
 ### Installation
 As easy as:
+- ```npm install --global grunt-cli``` [Grunt installation](http://gruntjs.com/getting-started)
 - ```npm install --global gulp-cli``` [Gulp installation](https://github.com/gulpjs/gulp)
 - ```npm install -g markdown-styleguide-generator``` [StyleGenerator installation](https://www.npmjs.com/package/markdown-styleguide-generator#install)
 - ```npm install```

package.json

@@ -29,6 +29,7 @@
     "node": ">= 0.8.0"
   },
   "devDependencies": {
+    "grunt": "~0.4.5",
     "jquery": "~2.2.0",
     "highlight.js": "~9.1.0",
     "markdown-styleguide-generator": "~2.0.4",
@@ -48,9 +49,6 @@
     "grunt-shell": "1.1.2",
     "load-grunt-tasks": "*"
   },
-  "peerDependencies": {
-    "grunt": "~0.4.5"
-  },
   "keywords": [
     "library",
     "CartoDB",