New formula: redshift

http://jonls.dk/redshift/
This doesn’t match:

```
$ curl -Ls https://github.com/jonls/redshift/archive/59023d86f4275128751bcb84ecda5a630bf51857.tar.gz | sha1sum
66a3a6011cdccb0b9ee77fde0de65da437c72ec5  -
```