Automatically ignore .gitignore files

[Ethan Diamond]

Hi! Prettier started automatically ignoring globs in .gitignore, and I thought that might be a good feature to add here as well. The logic is any files you wouldn't check in to git is generally not files that you control or would want to control, so ignore them by default saves some boilerplate. Any chance of having ls-lint do that as well?

[Lucas Löffel]

duplicate of #86