Update smoke tests to use both Rack 2 and 3 #135

Job	Run time
rubocop	13s
rspec (3.0)	36s
smoke_test (3.0, ~> 2)	30s
rspec (3.1)	35s
active_record_with_lock_adapter_rspec (3.0)	36s
smoke_test (3.0, ~> 3)	36s
rspec (3.2)	39s
active_record_with_lock_adapter_rspec (3.1)	36s
smoke_test (3.1, ~> 2)	52s
rspec (3.3)	37s
active_record_with_lock_adapter_rspec (3.2)	35s
smoke_test (3.1, ~> 3)	46s
active_record_with_lock_adapter_rspec (3.3)	40s
smoke_test (3.2, ~> 2)	51s
smoke_test (3.2, ~> 3)	52s
smoke_test (3.3, ~> 2)	53s
smoke_test (3.3, ~> 3)	51s
	11m 18s

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