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.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@6.2.0...6.4.1)

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

yarn.lock

@@ -619,9 +619,9 @@ acorn-walk@^6.0.1:
   integrity sha512-7evsyfH1cLOCdAzZAd43Cic04yKydNx0cF+7tiA19p1XnLLPU4dpCQOqpjqwokFe//vS0QqfqqjCS2JkiIs0cA==
 
 acorn@^6.0.1:
-  version "6.2.0"
-  resolved "https://registry.npmjs.org/acorn/-/acorn-6.2.0.tgz#67f0da2fc339d6cfb5d6fb244fd449f33cd8bbe3"
-  integrity sha512-8oe72N3WPMjA+2zVG71Ia0nXZ8DpQH+QyyHO+p06jT8eg8FGG3FbcUIi8KziHlAfheJQZeoqbvq1mQSQHXKYLw==
+  version "6.4.1"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.1.tgz#531e58ba3f51b9dacb9a6646ca4debf5b14ca474"
+  integrity sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==
 
 acorn@^7.1.0:
   version "7.1.0"