Try adding the http: part infront of the jQuery framework link - see below (works for me)
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
FWIW - Never sure why they give the link as just //ajax.etc because it never works and confuses loads of people. I guess just another bunch on tossers at large.
On a persoanl level I much prefer to have the jQuery framework script housed on my own server rather than llnking to an external source.
Also you have the 'Scroll To Top' link located only 75px from the top of the browser window....is that what you want?
