Upgrade mongodb to v3

[stevenschobert]

This doesn't have any breaking API changes, however the mongo upgrade is a major version bump, so that could cause some indirect breaking changes.

Changes

→ MongoDB Release Notes

Notably, the connection strings must not be URL encoded:

Following changes to the MongoDB connection string specification, authentication and hostname details in connection strings must now be URL-encoded. These changes reduce ambiguity in connection strings.

For example, whereas before mongodb://u$ername:pa$$w{}rd@/tmp/mongodb-27017.sock/test would have been a valid connection string (with username u$ername, password pa$$w{}rd, host /tmp/mongodb-27017.sock and auth database test), the connection string for those details would now have to be provided to MongoClient as mongodb://u%24ername:pa%24%24w%7B%7Drd@%2Ftmp%2Fmongodb-27017.sock/test.

There is also a small edge case the if you are using the find() method on a collection, you'll need to specify the type at the calling site:

// before
Model.getCollection()
  .find({ _id: 'someid' })
  .limit(1)
  .next();

// after
Model.getCollection()
  .find<any>({ _id: 'someid' })
  .limit(1)
  .next();

[etsuo]

related to: #112