[Security] Bump acorn from 6.2.0 to 6.4.1

Bumps [acorn](https://github.com/acornjs/acorn) from 6.2.0 to 6.4.1. **This update includes a security fix.**
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](https://github.com/acornjs/acorn/compare/6.2.0...6.4.1)

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

package-lock.json

@@ -24,9 +24,9 @@
       }
     },
     "acorn": {
-      "version": "6.2.0",
-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.2.0.tgz",
-      "integrity": "sha512-8oe72N3WPMjA+2zVG71Ia0nXZ8DpQH+QyyHO+p06jT8eg8FGG3FbcUIi8KziHlAfheJQZeoqbvq1mQSQHXKYLw==",
+      "version": "6.4.1",
+      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.4.1.tgz",
+      "integrity": "sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==",
       "dev": true
     },
     "builtin-modules": {