Fixed `cygapt.utils.rmtree` for Windows

| Q             | A
| ------------- | ---
| Bug fix?      | yes (Windows)
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Related tickets | 
| License       | GNU GPL v3

On Window the write permission for delete a path is also needed.