Bump async from 3.2.0 to 3.2.4

Bumps [async](https://github.com/caolan/async) from 3.2.0 to 3.2.4.
- [Release notes](https://github.com/caolan/async/releases)
- [Changelog](https://github.com/caolan/async/blob/master/CHANGELOG.md)
- [Commits](caolan/async@v3.2.0...v3.2.4)

---
updated-dependencies:
- dependency-name: async
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

package-lock.json

@@ -35,7 +35,7 @@
     "url": "https://github.com/smashwilson/hubot-markov/issues"
   },
   "dependencies": {
-    "async": "3.2.0",
+    "async": "3.2.4",
     "coffee-script": "~1.12.7",
     "pg-promise": "^10.1.0",
     "redis": "~3.1.0"