Match Windows directories with forward slashes

I had an edge case with absolute paths on Windows. After several Browserify transforms, I was ultimately requiring a filepath like,

    D:/some/project/directory/file.js

Admittedly that is a strange looking path, because it's using forward slashes with a Windows drive letter. However, I cross-referenced `require.resolve` and it handled it correctly, so I thought I would track down the discrepancy in `node-resolve`. The path was not matching the regex used to differentiate files from modules. Adding a small _or_ to the regex seems to solve this for me.