Bump acorn from 6.4.0 to 6.4.1

Bumps [acorn](https://github.com/acornjs/acorn) from 6.4.0 to 6.4.1.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](https://github.com/acornjs/acorn/compare/6.4.0...6.4.1)

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

package-lock.json

@@ -1497,9 +1497,9 @@
       }
     },
     "acorn": {
-      "version": "6.4.0",
-      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.4.0.tgz",
-      "integrity": "sha512-gac8OEcQ2Li1dxIEWGZzsp2BitJxwkwcOm0zHAJLcPJaVvm58FRnk6RkuLRpU1EujipU2ZFODv2P9DLMfnV8mw==",
+      "version": "6.4.1",
+      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.4.1.tgz",
+      "integrity": "sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==",
       "dev": true
     },
     "agentkeepalive": {