Remove unnecessary octal literal to allow the code to run in strict mode

Currently, attempting to run an application that depends upon this module in global strict mode (via the `--use-strict` flag) fails, due to the use of an octal literal.

Removing the octal literal fixes this issue, and does not cause any problems since the `0666` value being used is the default value according to the Node [file system documentation](http://nodejs.org/api/fs.html#fs_fs_open_path_flags_mode_callback) (this is true for all versions of Node supported by this module):

> **fs.open(path, flags, [mode], [callback])**
> ...
> `mode` defaults to `0666`