Fix typos in controller guidelines

[mcmire]

Explanation

See diff.

References

None — just something I noticed while re-reading over the guidelines.

Changelog

N/A

Checklist

• [x] I've updated the test suite for new or updated code as appropriate
• [x] I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• [x] I've highlighted breaking changes using the "BREAKING" category above as appropriate
• [x] I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes