Fix micromark-build in dev folders

[puqeko]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

Problem: Cloning micromark (main branch) into ~/dev/ (or any path containing /dev/) and running npm install && npm run build fails with Cannot find module....

Cause: micromark-build replaces the first occurrence of /dev/ in the full file path instead of the last occurrence when moving .js files up a directory.

Proposed Solution: This PR adds a negative lookahead to the regular expression in .replace so that the last occurrence of /dev/ is replaced correctly.

[wooorm]

Thanks! :)