Update vendored gems.

[reitermarkus]

• 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?
• Have you successfully run brew man locally and committed any changes?

[reitermarkus]

Reverted to RuboCop 0.92 for now since 0.93 is currently broken (rubocop/rubocop#8872).

[MikeMcQuaid]

Out of interest: why didn't Dependabot handle this for us?

[reitermarkus]

Hmm, seems like the YAML is invalid.