Update connection.rb

Fix for the following error,
--
/var/lib/gems/2.1.0/gems/obd-0.0.2/lib/obd/command.rb:4:in `initialize': wrong number of arguments (1 for 0) (ArgumentError)
	from /var/lib/gems/2.1.0/gems/obd-0.0.2/lib/obd/connection.rb:27:in `new'
	from /var/lib/gems/2.1.0/gems/obd-0.0.2/lib/obd/connection.rb:27:in `[]'
--