fixing cfn test -- --tb=long README docs (#826)

Author: PatMyron

README.md

@@ -53,7 +53,7 @@ To run the contract tests for a resource type, use the `test` command.
 ```bash
 cfn test
 cfn test -- -k contract_delete_update #to run a single test
-cfn test --tb=long #exhaustive, informative traceback formatting
+cfn test -- --tb=long #exhaustive, informative traceback formatting
 cfn test --enforce-timeout 60 #set the RL handler timeout to 60 seconds and CUD handler timeout to 120 seconds.
 cfn test --enforce-timeout 60 -- -k contract_delete_update # combine args
 cfn test --log-group-name cw_log_group --log-role-arn log_delivery_role_arn # Handler logs generated by contract tests will be delivered to the specified cw_log_group using the credentials from log_delivery_role_arn