Update Google fonts link to protocol relative url

I make a change in index.html. I changed the Google CSS link from http://fonts.googleapis.com/css?family=Open+Sans:300,400,700 to //fonts.googleapis.com/css?family=Open+Sans:300,400,700 (protocol relative URL), so that users can view that page over HTTPS.
Merge pull request #13 from nextPrime/master

Update Google fonts link to protocol relative url