DataOutputSchema addition

This adds possibility of validation workflow output in a similar way
that is already done for workflow input

See issue #611

Signed-off-by: Francisco Javier Tirado Sarti <ftirados@redhat.com>

Author: fjtirado

specification.md

@@ -1867,9 +1867,9 @@ a starting [Event state](#Event-state), it is not used to validate its event pay
 
 The `dataOutputSchema` property validates the [Workflow data output](#workflow-data-output). Validation should be performed when the process is finished. 
 
-Both properties can be expressed as object or string types. 
+Both properties can be expressed as object or string type. 
 
-If it is an object type, their `schema` property can be an URI, which points to the JSON schema used to validate the workflow data input, or it can be the JSON schema object. Their `failOnValidationErrors` property  determines if workflow execution should continue in case of validation errors. The default value of `failOnValidationErrors` is `true`.
+If using object type, their `schema` property might be an URI, which points to the JSON schema used to validate the workflow data input, or it might be the JSON schema object. Their `failOnValidationErrors` property  determines if workflow execution should continue in case of validation errors. The default value of `failOnValidationErrors` is `true`.
 
 Example for Json schema reference