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>

yarn.lock

@@ -916,8 +916,8 @@ acorn-jsx@^5.0.0:
   resolved "https://registry.yarnpkg.com/acorn-jsx/-/acorn-jsx-5.0.2.tgz#84b68ea44b373c4f8686023a551f61a21b7c4a4f"
 
 acorn@^6.0.7, acorn@^6.2.1:
-  version "6.3.0"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.3.0.tgz#0087509119ffa4fc0a0041d1e93a417e68cb856e"
+  version "6.4.1"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.1.tgz#531e58ba3f51b9dacb9a6646ca4debf5b14ca474"
 
 ajv-errors@^1.0.0:
   version "1.0.1"