Add protocol for jQuery to work when accessed as file

URLs without protocols get "file:" prepended when their document is
loaded as a file. Make sure the docs can always be opened by
specifying a protocol.

_includes/footer.html

 <!-- Bootstrap core JavaScript
 ================================================== -->
 <!-- Placed at the end of the document so the pages load faster -->
-<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
+<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
 <script src="{{ page.base_url }}dist/js/bootstrap.js"></script>
 
 <script src="{{ page.base_url }}docs-assets/js/holder.js"></script>