Downgrade jQuery to avoid DOM Exception 12 in getJSON() under Jasmine.

jQuery 2.0.x is throwing an error in getJSON() when run under a Jasmine
environment like the one in this commit.

The parent commit has jQuery 2.0.x and a commented debugger statement in
`js/lib/promises.js` to show the error.

Stack trace
-----------

```
Error: An invalid or illegal string was specified.
  at Object.x.support.cors.e.crossDomain.send (http://localhost:8001/js/vendor/jquery.js:6:8988)
  at Function.x.extend.ajax (http://localhost:8001/js/vendor/jquery.js:6:4804)
  at getJSON (http://localhost:8001/js/lib/promises.js:2:7)
  at null.<anonymous> (http://localhost:8001/js/test/promises.js:6:5)
  at http://localhost:8001/js/vendor/jasmine.js:1902:29
  at attempt (http://localhost:8001/js/vendor/jasmine.js:1910:7)
  at jasmine.QueueRunner.run (http://localhost:8001/js/vendor/jasmine.js:1902:5)
  at queueRunnerFactory [as queueRunner] (http://localhost:8001/js/vendor/jasmine.js:686:40)
  at jasmine.Spec.execute (http://localhost:8001/js/vendor/jasmine.js:506:8)
  at null.<anonymous> (http://localhost:8001/js/vendor/jasmine.js:2047:13)
```