add macOs as a option or always ignore .ds_store files

[Glenn-Terjesen]

Hi!
Can you add macOs as a option?
https://www.toptal.com/developers/gitignore/api/macos

or remove the noisy .ds_store files as default :-)

[jonschlinkert]

Honestly, I think I'd rather do the latter. I always have to add .DS_Store to gitignore files, no matter what I'm doing.

I'm not sure what the best approach to doing this should be in the generator. (fwiw I completely refactored Generate and many of the generators, including this one. The new code is a lot simpler). Suggestions welcome