move test to avoid DST weirdness in Samoa

This should be viewed in the context of #952 and #989, but I figured I'd just submit it separately, since it's an easy one. This is a test failure from Pacific/Apia that results from them [never leaving DST in 2010](http://www.timeanddate.com/worldclock/timezone.html?n=282):

```
Testing diff.js........F....
>> diff - diff between utc and local
>> Message: year diff
>> Error: year diff
>> at Object.exports.diff.diff between utc and local (test/moment/diff.js:173:14)
```

I just used a different year.