Fix operator precedence issue.
Fix operator precedence issue.

Noticed this when a filter was not invalidating its cache when a file was renamed (different name, same mtime and content): https://s3.amazonaws.com/f.cl.ly/items/3e3v1i0a3a3x10331X2r/Screen%20Shot%202015-05-14%20at%2010.58.23%20AM.png

Smaller expression of the issue:

```
> true === false && true ? 'ternary is true' : 'ternary is false, shouldn't get here'
'ternary is false, shouldn't get here'
> true === false && (true ? 'ternary is true' : 'ternary is false')
false
```
ember-cli/broccoli-caching-writer,jasonmit/broccoli-caching-writer,joliss/broccoli-caching-writer,chadhietala/broccoli-caching-writer