build(deps): bump acorn from 6.1.0 to 6.4.2
build(deps): bump acorn from 6.1.0 to 6.4.2

Bumps [acorn](https://github.com/acornjs/acorn) from 6.1.0 to 6.4.2.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](https://github.com/acornjs/acorn/compare/6.1.0...6.4.2)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>

apiaryio/pagerduty-overlap-checker,apiaryio/pagerduty-overlap-checker