MongoDB v4 support

[stephengardner]

What's the compatibility, here? Is it incompatible, or "it depends"? This is becoming quite necessary as cloud providers update their drivers to MongoDB 4.

[amit777]

the mongodb node lib version required for monk is 3.2.6. Mongoose uses 3.6.6. It seems monk's dependency is significantly behind. I'm researching monk to replace mongoose at the moment, but these old version of mongodb dependency is giving pause.