Updated dependences to work with latest mongodb and bcrypt

[beartastic]

latest mongodb no longer returns a db, but a client. Need to then pull db object.

[ghost]

Hey @beartastic, thanks for useful fork!

Since you've introduced 3.x version of Mongo driver, it produces several warnings due to API deprecations:

(node:11682) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
(node:11682) DeprecationWarning: collection.ensureIndex is deprecated. Use createIndexes instead.
(node:11682) DeprecationWarning: collection.update is deprecated. Use updateOne, updateMany, or bulkWrite instead.
(node:11682) DeprecationWarning: collection.remove is deprecated. Use deleteOne, deleteMany, or bulkWrite instead.

The first one can be surpassed by passing appropriate option to MongoStore constructor in consumer code, but latter ones should be updated inside library.

Would you consider updating it by yourself or should I make another PR from my fork?