append build revision to stylesheet path to break cache

_layouts/default.html

@@ -6,7 +6,7 @@
     <title>{{ site.title | default: site.github.repository_name }} by {{ site.github.owner_name }}</title>
 
     <link href='https://fonts.googleapis.com/css?family=Lato:300italic,700italic,300,700' 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 }}">
     <script src="{{ '/assets/js/scale.fix.js' | relative_url }}"></script>
     <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">