Allow "non-files" to be ignored

The resolve module correctly lists all core modules, e.g. assert,
crypto, os, etc.

However, browser-resolve does not provide implementations for all of
them.

It is valid for browserify to take non-files as arguments to ignore
as a way to work around this issue.

Modules like "os" can now be marked as ignored and grunt-browserify
will now pass these options them properly.

Signed-off-by: Joshua Rubin <jrubin@zvelo.com>