Bump async in /samples/react-custompropertypanecontrols

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>

samples/react-custompropertypanecontrols/package-lock.json

@@ -6876,9 +6876,9 @@
       "dev": true
     },
     "async": {
-      "version": "2.6.3",
-      "resolved": "https://onedrive.pkgs.visualstudio.com/_packaging/odsp-npm/npm/registry/async/-/async-2.6.3.tgz",
-      "integrity": "sha1-1yYl4jRKNlbjo61Pp0n6gymdgv8=",
+      "version": "2.6.4",
+      "resolved": "https://registry.npmjs.org/async/-/async-2.6.4.tgz",
+      "integrity": "sha512-mzo5dfJYwAn29PeiJ0zvwTo04zj8HDJj0Mn8TD7sno7q12prdbnasKJHhkm2c1LgrhlJ0teaea8860oxi51mGA==",
       "dev": true,
       "requires": {
         "lodash": "^4.17.14"