adding confidence.js to cdnjs

# Confidence.js

**Confidence.js** is a light-weight JavaScript library to help you make sense of your [A/B Test](http://en.wikipedia.org/wiki/A/B_testing) results. Given an A/B test (or "Split Test") result set, Confidence.js will tell you if a statistical "winner" can be determined.

I am just adding the library to cdnjs, I am not the author of this library.
Here is the github page: https://github.com/sendwithus/confidence