tweak template to fix search

Author: runestonetest

runestone/common/project_template/_templates/plugin_layouts/sphinx_bootstrap/layout.html

@@ -298,7 +298,7 @@
 
 <div class="container" id="continue-reading"></div>
 
-<div class="container" id="main-content">
+<div class="container" id="main-content" role="main">
   {% block body %}
   {% endblock %}
   <div id=scprogresscontainer>