[Security] Bump acorn from 6.4.0 to 6.4.1 (nodegui#62)

Bumps [acorn](https://github.com/acornjs/acorn) from 6.4.0 to 6.4.1. **This update includes a security fix.**
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@6.4.0...6.4.1)

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Author: dependabot-preview[bot]