Bump async from 2.6.3 to 2.6.4

Bumps [async](https://github.com/caolan/async) from 2.6.3 to 2.6.4.
- [Release notes](https://github.com/caolan/async/releases)
- [Changelog](https://github.com/caolan/async/blob/v2.6.4/CHANGELOG.md)
- [Commits](https://github.com/caolan/async/compare/v2.6.3...v2.6.4)

---
updated-dependencies:
- dependency-name: async
  dependency-type: indirect
...

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

yarn.lock

@@ -2286,8 +2286,8 @@ async-limiter@~1.0.0:
   resolved "https://registry.npmjs.org/async-limiter/-/async-limiter-1.0.1.tgz"
 
 async@^2.6.2:
-  version "2.6.3"
-  resolved "https://registry.npmjs.org/async/-/async-2.6.3.tgz"
+  version "2.6.4"
+  resolved "https://registry.yarnpkg.com/async/-/async-2.6.4.tgz#706b7ff6084664cd7eae713f6f965433b5504221"
   dependencies:
     lodash "^4.17.14"