fix css reference in DataTool.html

docs/DataTool.html

@@ -5,7 +5,7 @@
 	<title>Data Tool Online</title>
 	<meta charset="utf-8" />
 	<meta name="viewport" content="width=device-width, initial-scale=1">
-	<link rel="stylesheet" type="text/css" href="../tracker/css/library.css" />
+	<link rel="stylesheet" type="text/css" href="https://opensourcephysics.github.io/tracker-website/css/library.css" />
 	<script src="compadre.js"></script>
 	<script src="swingjs/swingjs2.js"></script>
 	<script>