Avoid polluting global namespace with `nodeFileReady` function

In the current version of Caman the `nodeFileReady` function is polluting the global namespace.

I'm not very confident with CoffeeScript so this commit may not be the best/valid way of correcting this bug. Actually, I'm quite confused with `->` and `=>` mentioned in the commit above the line 110. Please double-check before merging it. Thanks :)