bug (windows): diplicated items in list of available generators

On Windows, when I called `slush --help` I saw something like this

```bash
[slush] Installed generators
[slush] ├── angular (0.3.3)
[slush] ├── coffee (0.1.0)
[slush] ├── angular (0.3.3)
[slush] ├── coffee (0.1.0)
[slush] ├── angular (0.3.3)
[slush] └── coffee (0.1.0)
```

It happens because `getModulesPaths` generate array with duplicated paths and they need to be filtered.