Bump acorn from 6.3.0 to 6.4.1

Bumps [acorn](https://github.com/acornjs/acorn) from 6.3.0 to 6.4.1.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@6.3.0...6.4.1)

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

Author: dependabot[bot]

yarn.lock

@@ -1249,9 +1249,9 @@ acorn-walk@^6.1.1:
   integrity sha1-Ejy487hMIXHx9/slJhWxx4prGow=
 
 acorn@^6.0.7, acorn@^6.1.1, acorn@^6.2.1:
-  version "6.3.0"
-  resolved "https://registry.npm.taobao.org/acorn/download/acorn-6.3.0.tgz#0087509119ffa4fc0a0041d1e93a417e68cb856e"
-  integrity sha1-AIdQkRn/pPwKAEHR6TpBfmjLhW4=
+  version "6.4.1"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.1.tgz#531e58ba3f51b9dacb9a6646ca4debf5b14ca474"
+  integrity sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==
 
 address@^1.0.3:
   version "1.1.2"