Add MacScale latest

- class name now == Macscale as per [Naming
Ref](https://github.com/caskroom/homebrew-cask/blob/master/doc/CASK_NAMING_REFERENCE.md)
- version now == :latest and sha256 == :no_check as per. [Contributing](https://github.com/caskroom/homebrew-cask/blob/master/CONTRIBUTING.md#cask-stanzas)
Merge pull request #6502 from jm3/macscale

Add MacScale 1.6.4