fix missing quotation mark in notebook.html

IPython/frontend/html/notebook/templates/notebook.html

@@ -245,6 +245,6 @@ data-notebook-id={{notebook_id}}
 <script src="{{ static_url("js/tooltip.js") }}" type="text/javascript" charset="utf-8"></script>
 <script src="{{ static_url("js/notebookmain.js") }}" type="text/javascript" charset="utf-8"></script>
 
-<script src="{{ static_url("js/contexthint.js") }} charset="utf-8"></script>
+<script src="{{ static_url("js/contexthint.js") }}" charset="utf-8"></script>
 
 {% end %}