Incorrect paths on Windows

[mglaman]

I was working on mglaman/drupal-check#189 and noticed that weird paths were returned in realpath was called for the Drupal path.

Analyzing path: C:\projects\drupal\web\core\install.php
Using Drupal root: C:\projects\drupal/web
Using vendor root: C:\projects\drupal/vendor

The web and vendor paths have /. I know PHP fixes incorrect directory separators most of the time. But in AppVeyor I get crashes like

The filename, directory name, or volume label syntax is incorrect.
``

And I think it's because `cmd` chokes on `/`.