hubotio/hubot

fix: address deprecation warning on startup

Brain: avoid retaining dangerous robot/brain references

Add a new persistence model - Datastore

Dependency updates

The Datastore class provides a persistent, database-backed key-value
data storage class. This complements the existing Brain class in a few
ways:

1. Each get/set operation is directly backed by the backing database,
   allowing multiple Hubot instances to share cooperative access to
   data simultaneously;
2. get/set operations are asynchronous, mapping well to the async
   access methods used by many database adapters.

Brain: ensure User objects are actually User objects

The default Hubot require entrypoint is only compatible with
CoffeeScript. A separate entrypoint has to be used when writing ES2015
classes.