Fix getJSON success function type jquery externs

This PR suggests to change the signature of the `success` function in the jquery externs files. Currently the type is `function(string,string,jQuery.jqXHR)=}`, which does not match what's documented in the [jQuery doc](http://api.jquery.com/jquery.getjson/#jQuery-getJSON-url-data-success). So this PR changes the annotation to `function(Object.<string,*>,string,jQuery.jqXHR)=`. At this point I've only changed jquery-1.9.js but I can change the other jquery externs files if you agree with the change.

Related to https://github.com/google/closure-compiler/issues/176.