Declare favicon in head

Author: Shuwen Qian

docs/head.html

@@ -7,6 +7,7 @@
 	<meta name="theme-color" content="#000000"/>
 	<meta name="viewport" content="width=device-width,minimum-scale=1,maximum-scale=1"/>
 	<title>Strand Web Components</title>
+	<link rel="icon" href="favicon.ico" type="image/x-icon" />
 	<script language="javascript" src="bower_components/webcomponentsjs/webcomponents-lite.js"></script>
 	<link rel="stylesheet" type="text/css" href="docs.css"/>
 	<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/8.8.0/styles/github.min.css">
@@ -18,4 +19,4 @@
 	<script language="javascript" src="//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script>
 	<script language="javascript" src="//cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>
 	<script language="javascript" src="//cdnjs.cloudflare.com/ajax/libs/highlight.js/8.8.0/highlight.min.js"></script>
-</head>
+</head>