Don't check if fs.access() exists, use it for fs.exists()

[RyanZim]

Since we're not supporting Node versions less than v4, there's no reason to check if fs.access() exists.

Also changed fs.exists to use access, since I believe I heard it's faster.

[coveralls]

Coverage decreased (-0.2%) to 92.0% when pulling f641bb8 on RyanZim:access into 9aea3f5 on normalize:master.

[dead-horse]

we haven't declare node version in package.json, so it is support less than v4 now.

[RyanZim]

Gotcha, just assumed you only supported Node 4+ due to the .travis.yml