append build revision to stylesheet path to break cache

Author: benbalter

Diff for: _layouts/default.html

@@ -6,7 +6,7 @@
     <meta http-equiv="X-UA-Compatible" content="chrome=1">
     <meta name="description" content="{{ site.title | default: site.github.repository_name }} : {{ site.description | default: site.github.project_tagline }}">
 
-    <link rel="stylesheet" type="text/css" media="screen" href="{{ '/assets/css/style.css' | relative_url }}">
+    <link rel="stylesheet" type="text/css" media="screen" href="{{ '/assets/css/style.css?v=' | append: site.github.build_revision | relative_url }}">
 
     <title>{{ site.title | default: site.github.repository_name }}</title>
   </head>