chore(deps): bump acorn from 6.2.1 to 6.4.1

Bumps [acorn](https://github.com/acornjs/acorn) from 6.2.1 to 6.4.1.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](https://github.com/acornjs/acorn/compare/6.2.1...6.4.1)

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

yarn.lock

@@ -1790,9 +1790,9 @@ acorn-walk@^6.1.1:
   integrity sha512-7evsyfH1cLOCdAzZAd43Cic04yKydNx0cF+7tiA19p1XnLLPU4dpCQOqpjqwokFe//vS0QqfqqjCS2JkiIs0cA==
 
 acorn@^6.0.2, acorn@^6.0.7, acorn@^6.2.1:
-  version "6.2.1"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.2.1.tgz#3ed8422d6dec09e6121cc7a843ca86a330a86b51"
-  integrity sha512-JD0xT5FCRDNyjDda3Lrg/IxFscp9q4tiYtxE1/nOzlKCk7hIRuYjhq1kCNkbPjMRMZuFq20HNQn1I9k8Oj0E+Q==
+  version "6.4.1"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.1.tgz#531e58ba3f51b9dacb9a6646ca4debf5b14ca474"
+  integrity sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==
 
 after@0.8.2:
   version "0.8.2"