Bump async from 2.6.3 to 3.1.0 (#158)

Bumps [async](https://github.com/caolan/async) from 2.6.3 to 3.1.0.
- [Release notes](https://github.com/caolan/async/releases)
- [Changelog](https://github.com/caolan/async/blob/master/CHANGELOG.md)
- [Commits](caolan/async@v2.6.3...v3.1.0)

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

Author: dependabot-preview[bot]

package.json

@@ -21,7 +21,7 @@
   },
   "dependencies": {
     "ampersand-state": "^5.0.3",
-    "async": "^2.1.2",
+    "async": "^3.1.0",
     "chalk": "^2.1.0",
     "debug": ">= 2.6.9 < 3.0.0 || >= ^3.1.0",
     "docopt": "^0.6.2",