Bump acorn from 6.1.1 to 6.4.1

Bumps [acorn](https://github.com/acornjs/acorn) from 6.1.1 to 6.4.1.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](https://github.com/acornjs/acorn/compare/6.1.1...6.4.1)

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

package-lock.json

@@ -1029,9 +1029,9 @@
             }
         },
         "acorn": {
-            "version": "6.1.1",
-            "resolved": "http://registry.npm.taobao.org/acorn/download/acorn-6.1.1.tgz",
-            "integrity": "sha1-fSWuBbuK0fm2mRCOEJTs14hK3B8=",
+            "version": "6.4.1",
+            "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.4.1.tgz",
+            "integrity": "sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==",
             "dev": true
         },
         "acorn-dynamic-import": {