append build revision to stylesheet path to break cache

_layouts/default.html

@@ -4,7 +4,7 @@
     <meta charset="utf-8">
     <meta http-equiv="X-UA-Compatible" content="chrome=1">
     <title>{{ site.title | default: site.github.repository_name }} by {{ site.github.owner_name }}</title>
-    <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 }}">
     <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
     <script src="{{ '/assets/js/respond.js' | relative_url }}"></script>
     <!--[if lt IE 9]>