path.relative regression in v5.7.0

```
> var path = require('path');
> path.relative('/home/foo/bar', '/home/foo')
"../../foo"
```

Expected output is "..", which is what happens in v5.5.0, v4.3.1, v0.12.10 and v0.10.42.
- **Version**: _v5.7.0_
- **Platform**: _Linux 4.0.5-gentoo SMP PREEMPT Mon Sep 14 14:30:27 CEST 2015 x86_64 Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz GenuineIntel GNU/Linux_
- **Subsystem**: _path_
