Fix database in redis url

This MR fixes Redis connection. When a db is specified in a url, it is correctly set in client but not connection.

Example:

redis = Redis.new(url: 'redis://localhost?db=4')

redis.client.options[:url]
=> "redis://localhost?db=4" # this is correct

 redis.connection
=> {:host=>"localhost", :port=>6379, :db=>0, :id=>"redis://localhost:6379/0", :location=>"localhost:6379"} # db here is incorrect

When the db is passed as a separated option, it works:

redis = Redis.new(url: 'redis://localhost?db=4', db: 4)

redis.client.options[:url]
=> "redis://localhost?db=4"

redis.connection
=> {:host=>"localhost", :port=>6379, :db=>4, :id=>"redis://localhost:6379/4", :location=>"localhost:6379"}