Merge pull request jupyter#296 from ellisonbg/fix-css-cache

Add cache busting for GH pages.

Author: ellisonbg

Diff for: _includes/head.html

@@ -13,7 +13,7 @@
     <meta property="og:image" content="http://jupyter.org/assets/homepage.png" />
     <!-- Bootstrap Core CSS -->
     <link rel="stylesheet" href="{{ "/css/bootstrap.min.css" | prepend: site.baseurl }}">
-    <link rel="stylesheet" href="{{ "/css/logo-nav.css" | prepend: site.baseurl }}">
+    <link rel="stylesheet" href="{{ "/css/logo-nav.css" | prepend: site.baseurl }}?{{site.time | date: '%s%N'}}">
     <link rel="stylesheet" href="{{ "/css/cardlist.css" | prepend: site.baseurl }}">
     <link rel="stylesheet" href="{{ "/css/github-buttons.css" | prepend: site.baseurl }}">
     <link rel="icon" type="image/png" href="favicon.ico" />