mage is now available in scoop (package manager for Windows)

Besides being [available in brew](https://github.com/magefile/mage/issues/288) for Linux/MacOS users, now it also available in [scoop](https://scoop.sh/) for Windows users:
```
scoop install mage
```

Formula: [mage.json](https://github.com/ScoopInstaller/Main/blob/master/bucket/mage.json)

Related: #234