https://docs.mongodb.com/ruby-driver/master/tutorials/ruby-driver-create-client/#uri-options-conversions states:

maxStalenessSeconds=Integer => :max_staleness => Float

This is incorrect in two ways:

1. The setting is under :read options, not at top level.
2. Max staleness value is an integer, not a float.

Additionally, max_staleness is not documented as a Ruby option, and this should be remedied as part of this ticket.