Remove dependency on fs-plus to reduce load time

[chocolateboy]

This PR improves the responsiveness of coffee-cash by removing its dependency on fs-plus. It also expands the version range of the coffee-script dependency to include 1.9, 1.10 &c. (1.8.0 is over a year old).

In my particular use case, this yields a speedup of ~20 ms (15% of the total execution time, including node's slow startup, and > 50% of the application execution time). This is unlikely to be significant in Atom, but it can make a huge difference on the command line.

$ cat ./profile.js

require('time-require')
require('coffee-cash')

$ node ./profile.js