update rubocop configuration for CI

[rei-moo]

All PRs:

• [ ] Has tests
• [ ] Documentation updated

Adding a new header

Generally, adding a new header is always OK.

• Is the header supported by any user agent? If so, which?
• What does it do?
• What are the valid values for the header?
• Where does the specification live?

Adding a new CSP directive

• Is the directive supported by any user agent? If so, which?
• What does it do?
• What are the valid values for the directive?