Bump acorn from 6.0.5 to 7.4.1

Bumps [acorn](https://github.com/acornjs/acorn) from 6.0.5 to 7.4.1.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@6.0.5...7.4.1)

---
updated-dependencies:
- dependency-name: acorn
  dependency-type: indirect
...

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Author: dependabot[bot]