Use platform-independent absolute paths

This resolves issues caused by having a path with both forward and backslashes (especially on Win32 as the hardcoded paths were for *nix).

I believe this was the cause of the following [SO question](http://stackoverflow.com/questions/25579734/nodejs-google-api-module-version-v2-not-found), however, being fully Mac-centric, I currently have no means to test this (at least on OS X everything still works :-) ).

I have regenerated the apis/index.js file so hopefully a new patch release will do the trick.