Bump async from 2.6.0 to 2.6.4 in /turbo-resolver

Bumps [async](https://github.com/caolan/async) from 2.6.0 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@v2.6.0...v2.6.4)

---
updated-dependencies:
- dependency-name: async
  dependency-type: direct:production
...

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

turbo-resolver/package.json

@@ -7,7 +7,7 @@
     "url": "https://github.com/stackblitz/core.git"
   },
   "dependencies": {
-    "async": "^2.6.0",
+    "async": "^2.6.4",
     "graphlib": "^2.1.5",
     "npm-package-arg": "^6.0.0",
     "semver": "^5.5.0",