Bumps [acorn](https://github.com/acornjs/acorn) from 3.3.0 to 6.4.1.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@3.3.0...6.4.1)

Signed-off-by: dependabot[bot] <support@github.com>