Fix test failure on Chrome 33

I'm seeing the following test failure on OSX Chrome 33.0.1750.117 (the same test passes in Safari).

```
Error: expected 8399737.88981836 to be within 1e-9 of 8399737.889818361
    at Assertion.assert (http://localhost:3000/test/expect-0.2.0-ol3/expect.js:99:13)
    at Assertion.roughlyEqual.Assertion.kindaEqual (http://localhost:3000/test/expect-0.2.0-ol3/expect.js:494:10)
    at Context.<anonymous> (http://localhost:3000/test/loader.js/Users/tschaub/projects/ol3/test/spec/ol/extent.test.js:237:39)
    at Test.Runnable.run (http://localhost:3000/test/mocha-1.8.1/mocha.js:4053:32)
    at Runner.runTest (http://localhost:3000/test/mocha-1.8.1/mocha.js:4410:10)
    at http://localhost:3000/test/mocha-1.8.1/mocha.js:4456:12
    at next (http://localhost:3000/test/mocha-1.8.1/mocha.js:4336:14)
    at http://localhost:3000/test/mocha-1.8.1/mocha.js:4345:7
    at next (http://localhost:3000/test/mocha-1.8.1/mocha.js:4293:23)
    at http://localhost:3000/test/mocha-1.8.1/mocha.js:4313:5
```