Update index.html to provide mime type for script.js reference

Added type="text/javascript" to swipe.js script tag -- my Chrome (vanilla installed Version 35.0.1916.153 on Linux Mint) was not executing the script and issued the following error:

Refused to execute script from 'https://raw.github.com/bradbirdsall/Swipe/master/swipe.js' because its MIME type ('text/plain') is not executable, and strict MIME type checking is enabled.