🎁 Pull Request

• Used a clear / meaningful title for this pull request
• Tested the changes in your own code (on your projects)
• Added / Edited tests to reflect changes (tests folder)
• Have read the Contributing part of the Readme
• Passed npm test

Fixes

fixes #258

Why have you made changes?

Join didn't work with readonly arrays

What changes have you made?

• added readonly keyword to arrays checked by the _Join conditional type

What tests have you updated?

• JOIN in tests/String.ts

Is there any breaking changes?

• Yes, I changed the public API & documented it
• Yes, I changed existing tests
• No, I added to the public API & documented it
• No, I added to the existing tests
• I don't know

Anything else worth mentioning?