Update to GSAP 1.13.1

- Reordered the order in which the default selector was determined to more closely match versions prior to 1.13.0. If, for example, "$" referred to jQuery at the time TweenLite/Max loaded and then some other selector engine (like Zepto or Prototype) was loaded that hijacked "$", version 1.13.0 used the latter whereas earlier versions used the former. The goal here is to maximize compatibility with legacy code.

- Fixed minor compatibility problem with jquery.gsap.js plugin