docs(readme): Update required Grunt version

Update Grunt version: ~0.4.5 -> >=0.4.0

Author: ahmehri

README.md

@@ -7,7 +7,7 @@ Use [Grunt](http://gruntjs.com/) with
 to generate great documentation for your JavaScript projects.
 
 ## Getting Started
-This plugin requires Grunt `~0.4.5`
+This plugin requires Grunt `>=0.4.0`
 
 If you haven't used [Grunt](http://gruntjs.com/) before, be sure to check out the [Getting Started](http://gruntjs.com/getting-started) guide, as it explains how to create a [Gruntfile](http://gruntjs.com/sample-gruntfile) as well as install and use Grunt plugins. Once you're familiar with that process, you may install this plugin with this command: