Bump acorn from 6.0.7 to 6.4.1

Bumps [acorn](https://github.com/acornjs/acorn) from 6.0.7 to 6.4.1.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@6.0.7...6.4.1)

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

Author: dependabot[bot]

yarn.lock

@@ -24,9 +24,9 @@ acorn-jsx@^5.0.0:
   integrity sha512-HJ7CfNHrfJLlNTzIEUTj43LNWGkqpRLxm3YjAlcD0ACydk9XynzYsCBHxut+iqt+1aBXkx9UP/w/ZqMr13XIzg==
 
 acorn@^6.0.2:
-  version "6.0.7"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.0.7.tgz#490180ce18337270232d9488a44be83d9afb7fd3"
-  integrity sha512-HNJNgE60C9eOTgn974Tlp3dpLZdUr+SoxxDwPaY9J/kDNOLQTkaDgwBUXAF4SSsrAwD9RpdxuHK/EbuF+W9Ahw==
+  version "6.4.1"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.1.tgz#531e58ba3f51b9dacb9a6646ca4debf5b14ca474"
+  integrity sha512-ZVA9k326Nwrj3Cj9jlh3wGFutC2ZornPNARZwsNYqQYgN0EsV2d53w5RN/co65Ohn4sUAUtb1rSUAOD6XN9idA==
 
 ajv@^6.5.3, ajv@^6.6.1:
   version "6.8.1"