Check docs are up to date

Please check if your documentation files are still up-to-date.

The key documentation files to check are:

- `docs/ABOUT.md`
- `docs/INSTALLATION.md`
- `docs/LEARNING.md`
- `docs/RESOURCES.md`
- `docs/TESTS.md`
- `exercises/shared/.docs/help.md`
- `exercises/shared/.docs/tests.md`

There might be more.

## Link check report

To help identify invalid links, we've automatically checked the links of _all_ `*.md` files in this repo.
This is the report of that check:

📝 Summary

---------------------

🔍 Total...........55

✅ Successful......53

⏳ Timeouts.........0

🔀 Redirected.......0

👻 Excluded.........0

🚫 Errors...........2


Errors in ./README.md

✗ https://gitter.im/exercism/erlang (HTTP status client error (404 Not Found) for url (https://gitter.im/exercism/erlang))

✗ https://gitter.im/exercism/erlang?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge (HTTP status client error (404 Not Found) for url (https://gitter.im/exercism/erlang?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge))

https://github.com/exercism/v3-launch/issues/54