'which nim' error on Windows
Hi,

Installation via **nimble** goes smoothly, but when running on Windows 10, I get:
```
INim 0.1.0
Nim Compiler Version 0.18.0 [Windows: i386]
Error: unhandled exception: The system cannot find the file specified.

Additional info: Requested command not found: 'which nim'. OS error: [OSError]
```
Shouldn't it be 'where nim' on Windows?