Fix broken fs.existsSync call when running on node 0.6

The existsSync method was correctly defined with `fs.existsSync || Path.existsSync` but there was a remaining call to `fs.existsSync`
Merge pull request #220 from abe33/patch-2

Fix broken fs.existsSync call when running on node 0.6

LGTM, thanks!
Preparing for release