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](caolan/async@v2.6.3...v2.6.4)

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

Signed-off-by: dependabot[bot] <[email protected]>

yarn.lock

@@ -1321,9 +1321,9 @@ astring@^1.4.3:
   integrity sha512-yJlJU/bmN820vL+cbWShu2YQU87dBP5V7BH2N4wODapRv27A2dZtUD0LgjP9lZENvPe9XRoSyWx+pZR6qKqNBw==
 
 async@^2.6.2:
-  version "2.6.3"
-  resolved "https://registry.yarnpkg.com/async/-/async-2.6.3.tgz#d72625e2344a3656e3a3ad4fa749fa83299d82ff"
-  integrity sha512-zflvls11DCy+dQWzTW2dzuilv8Z5X/pjfmZOWba6TNIVDm+2UDaJmXSOXlasHKfNBs8oo3M0aT50fDEWfKZjXg==
+  version "2.6.4"
+  resolved "https://registry.yarnpkg.com/async/-/async-2.6.4.tgz#706b7ff6084664cd7eae713f6f965433b5504221"
+  integrity sha512-mzo5dfJYwAn29PeiJ0zvwTo04zj8HDJj0Mn8TD7sno7q12prdbnasKJHhkm2c1LgrhlJ0teaea8860oxi51mGA==
   dependencies:
     lodash "^4.17.14"