chore(deps): bump acorn from 6.0.4 to 6.4.2

Bumps [acorn](https://github.com/acornjs/acorn) from 6.0.4 to 6.4.2.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@6.0.4...6.4.2)

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

Author: dependabot[bot]

yarn.lock

@@ -1641,9 +1641,9 @@ acorn-jsx@^5.0.0:
   integrity sha512-XkB50fn0MURDyww9+UYL3c1yLbOBz0ZFvrdYlGB8l+Ije1oSC75qAqrzSPjYQbdnQUzhlUGNKuesryAv0gxZOg==
 
 acorn@^6.0.2:
-  version "6.0.4"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.0.4.tgz#77377e7353b72ec5104550aa2d2097a2fd40b754"
-  integrity sha512-VY4i5EKSKkofY2I+6QLTbTTN/UvEQPCo6eiwzzSaSWfpaDhOmStMCMod6wmuPciNq+XS0faCglFu2lHZpdHUtg==
+  version "6.4.2"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.4.2.tgz#35866fd710528e92de10cf06016498e47e39e1e6"
+  integrity sha512-XtGIhXwF8YM8bJhGxG5kXgjkEuNGLTkoYqVE+KMR+aspr4KGYmKYg7yUe3KghyQ9yheNwLnjmzh/7+gfDBmHCQ==
 
 after@0.8.2:
   version "0.8.2"