Update foxmail.rb

```bash
Error: SHA2 mismatch
Expected: b71c373f96f69835ead265ab47957d3f81920025adeea0d37374415d0d03d06c
Actual: 164f1752d69dc8f4b9e9ee730ee5d55e2dd41f5f30507863b8292a1aee26e6ea
Archive: /Library/Caches/Homebrew/foxmail-1.2.0.dmg
To retry an incomplete download, remove the file above.
```