[Security] Bump acorn from 6.0.5 to 6.4.2

Bumps [acorn](https://github.com/acornjs/acorn) from 6.0.5 to 6.4.2. **This update includes security fixes.**
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@6.0.5...6.4.2)

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

Author: dependabot-preview[bot]

yarn.lock

@@ -1056,9 +1056,9 @@ acorn-jsx@^5.0.0:
   integrity sha512-HJ7CfNHrfJLlNTzIEUTj43LNWGkqpRLxm3YjAlcD0ACydk9XynzYsCBHxut+iqt+1aBXkx9UP/w/ZqMr13XIzg==
 
 acorn@^6.0.2:
-  version "6.0.5"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-6.0.5.tgz#81730c0815f3f3b34d8efa95cb7430965f4d887a"
-  integrity sha512-i33Zgp3XWtmZBMNvCr4azvOFeWVw1Rk6p3hfi3LUDvIFraOMywb1kAtrbi+med14m4Xfpqm3zRZMT+c0FNE7kg==
+  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"