Make `use-t-well` more auto-fixable #244

When https://github.com/avajs/eslint-plugin-ava/pull/229 is merged, use-t-well will be able to autofix falsey to falsy (a common misspell).

This can be expanded further by creating a small list of common misspells that can be autofixed (t.contxt, t.truthey, t.deepequal ...) I don't know what's the limit to the size of that list. It could even be allowed to customize it with an option.

Note: This issue has a bounty, so it's expected that you are an experienced programmer and that you give it your best effort if you intend to tackle this. Don't forget, if applicable, to add tests, docs (double-check for typos). And don't be sloppy. Review your own diff multiple times and try to find ways to improve and simplify your code. Instead of asking too many questions, present solutions. The point of an issue bounty is to reduce my workload, not give me more. Include a 🦄 in your PR description to indicate that you've read this. Thanks for helping out 🙌 - @sindresorhus