Fixing sorting bug in ga code.

Just a quick patch to get analytics sorting working.

I've also removed the behaviour where you were prefixing all sort values with an '-' to automatically reverse the sort direction. I feel that allowing access to both ASC and DESC ordering outweighs the advantage of being able to leave a single character out of the sort parameter.

PS. Big thanks to you for open sourcing this project. It is gold! Looking forward to adding more API integrations to it in the future.