Make JQuery reference scheme-agnostic

FF29/Chrome36 refuse to load jquery from non-https url specified when page is fetched over https (error: "[blocked] The page at 'https://emisfera.github.io/Splitchar.js/' was loaded over HTTPS, but ran insecure content from 'http://code.jquery.com/jquery-latest.min.js': this content should also be loaded over HTTPS.")

Discovered by accident with https-everywhere plugin forcing https on github.io pages.