Added a meta element to the header of the model document, per pubrule…

…s' checker

model/index.html

@@ -4,6 +4,7 @@
     <title>ODRL Information Model</title>
     <meta content="text/html; charset=utf-8" http-equiv="content-type" />
     <meta content="width=device-width,initial-scale=1" name="viewport" />
+    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no" />
     <script class="remove" src="https://www.w3.org/Tools/respec/respec-w3c-common" defer></script>
     <script class="remove" src="config.js"></script>
   </head>