Reword f.lux after_install comment

I'm going to work on some PRs to add `moveToApplicationsFolderAlertSuppress` to other casks but I was looking at the f.lux commit (fb19d4d) and thought the comment could be improved. The biggest problem to me is that the comment assumes the user is male. Here is a comment without gender pronouns that also has the benefit of being reusable for any cask, in the end I don't think it's useful to mention f.lux in the comment :)