feat: allow the word invalid for clearer error descriptions

[christophermorin]

Fixes Issue

Closes #748

Changes proposed

Allows the word 'invalid' to be used.

Check List (Check all the applicable boxes)

• My code follows the code style of this project.
• My change requires changes to the documentation.
• I have updated the documentation accordingly.
• All new and existing tests passed.
• This PR does not contain plagiarized content.
• The title of my pull request is a short description of the requested changes.

Screenshots

Note to reviewers

Please ignore if changing the banned words list is frowned upon. This seemed like an easier issue for a beginner so I had a crack at it.

[loftwah]

This looks good to me, although it isn't apparent why there are two lists of words. What is the difference between line 8 and line 13?

For example, fellow is found in both of them.