Date comparisons don't work in v-if/v-show

http://jsfiddle.net/5sH6A/92/

``` html
<div v-if="Date.now() < new Date('2020-01-01')">ASDFGASDFGASDFG</div>
<div v-if="Date.now() > new Date('2020-01-01')">QWERTQWERTQWERT</div>
```

Seems like it's converting  `new Date` into `newDate` and trying to look for both that and `Date` in the properties list in the current scope
