update to the 2.2.x version of Pusher's JavaScript library

Pusher has made two new releases with multiple fixes since April - see https://github.com/pusher/pusher-js/releases  This library is referencing an old version of Pusher's library.

I followed the contribution instructions in the README, but the gh-pages branch appears to have radically different code in the library.  The gh-pages branch doesn't have the `secureScriptUrl` variable from what I can tell.  I tried starting on that branch, but there were too many changes following the instructions, so I just changed the version numbers in the script files on master.  If gh-pages is the default branch for the contributions, is there a reason why the code is so different (and appears to be missing updates)?