fix(documentation): incorrect highlight references

[lcrockett]

Check list

• [X] I have read through the README (especially F.A.Q section)
• [ ] I have searched through the existing issues or pull requests
• [ ] I have verified all existing unit tests pass (See the README on how to run)
• [ ] I have added new tests if appropriate
• [ ] I have performed a self-review of my code and commented hard-to-understand areas
• [X] I have made corresponding changes to the documentation (when necessary)

Description

Incorrect highlight group references

Type of change

• [ ] Bug fix
• [ ] New feature
• [ ] Improvement of existing features
• [ ] Refactor
• [ ] Breaking change
• [X] Documentation change
• [ ] CI / CD

Test environment

• OS
  • [ ] Linux
  • [ ] Mac OS X
  • [ ] Windows
  • [ ] Others:
• Vim
  • [ ] Neovim:
  • [ ] Vim:

[ZNielsen]

Good catch, thank you!