Adding fallback font-family sans-serif (MithrilJS#2411)

Author: Showtim3

docs/style.css

@@ -1,5 +1,5 @@
 body {background:white;-webkit-text-size-adjust: 100%;}
-body,table,h5 {font:normal 16px 'Open Sans';}
+body,table,h5 {font-weight:normal;font-size:16px;font-family:'Open Sans',sans-serif;}
 header,main {margin:auto;max-width:1000px;}
 header section {position:absolute;width:250px;}
 nav a {border-left:1px solid #ddd;padding:0 10px;}