chmod recursively to satisfy zsh "insecure directories" warning

[phunehehe]

without -R only share is updated, leaving share/zsh/site-functions unchanged, so the warning won't go away

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

[reitermarkus]

Thanks, @phunehehe!