append build revision to stylesheet path to break cache

Author: benbalter

_layouts/default.html

@@ -4,7 +4,7 @@
     <meta charset='utf-8'>
     <meta http-equiv="X-UA-Compatible" content="chrome=1">
     <link href='https://fonts.googleapis.com/css?family=Chivo:900' rel='stylesheet' type='text/css'>
-    <link rel="stylesheet" href="{{ '/assets/css/style.css' | relative_url }}">
+    <link rel="stylesheet" href="{{ '/assets/css/style.css?v=' | append: site.github.build_revision | relative_url }}">
     <link rel="stylesheet" type="text/css" href="{{ '/assets/css/print.css' | relative_url }}" media="print">
     <!--[if lt IE 9]>
     <script src="//html5shiv.googlecode.com/svn/trunk/html5.js"></script>