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](acornjs/acorn@6.1.1...6.4.1)

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

Author: dependabot[bot]

yarn.lock

@@ -101,9 +101,9 @@ acorn-jsx@^5.0.0:
   integrity sha512-HJ7CfNHrfJLlNTzIEUTj43LNWGkqpRLxm3YjAlcD0ACydk9XynzYsCBHxut+iqt+1aBXkx9UP/w/ZqMr13XIzg==
 
 acorn@^6.0.7:
-  version "6.1.1"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.1.1.tgz#7d25ae05bb8ad1f9b699108e1094ecd7884adc1f"
-  integrity sha512-jPTiwtOxaHNaAPg/dmrJ/beuzLRnXtB0kQPQ8JpotKJgTB6rX6c8mlf315941pyjBSaPg8NHXS9fhP4u17DpGA==
+  version "6.4.1"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.1.tgz#531e58ba3f51b9dacb9a6646ca4debf5b14ca474"
+  integrity sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==
 
 ajv@^6.9.1:
   version "6.10.0"