= Check if isWindows properly

[tetreum]

Closes #2

[doowb]

Thanks for the PR!

Since the test is failing, I want to get @jonschlinkert's input on this. With this change, on linux and mac any path passed in will be invalid. Since the description states that it checks windows paths, I think this makes sense. To test on a non-windows OS, I think the tests just need to take an options object with { windows: true } so that the logic is tested.