added favicon link rel

data/force.html

@@ -1,6 +1,8 @@
 <!DOCTYPE hmtl>
 <meta charset="utf-8">
 <title>Collusion</title>
+<link rel="icon" href="favicon.ico" type="image/x-icon">
+<link rel="shortcut icon" href="favicon.ico" type="image/x-icon">
 <script src="d3.js"></script>
 <style>
 circle.node {