[DMN Designer] Marshaller - Decision Services are not being correctly persisted

Currently, decision services are missing the outputDecision property; without it the model doesn't work properly.

Consider this example:

• Traffic Violation updated.dmn: https://gist.github.com/karreiro/c9258a73751e54fe44c2630f6b5d7f37
• Example.dmn: https://gist.github.com/karreiro/eb6442a6bb95a427aeb5564dda458d46
• Client: https://gist.github.com/karreiro/d15873fe99a11b1088fbeaa799865c82

The execution of example.dmn doesn't work. However, adding <dmn:outputDecision href="#_8A408366-D8E9-4626-ABF3-5F69AA01F880"/> in the line 149 of the Traffic Violation updated.dmn fixes things.