Change property dateTime in logistics reference construct.

[larsolofsson]

format: date-time requires a timezone in OpenAPI

Current property dateTime in property references as specified in issue #317

          dateTime:
            type: string
            format: date-time
            description: |
              The dateTime when the referenced item was created or updated. 
              It MUST be local or UTC date-time expressed in ISO 8601

to be changed to

          dateTime:
            type: string
            minLength: 4
            description: |
              The dateTime when the referenced item was created or updated. 
              It MUST be local or UTC date-time expressed in ISO 8601

[larsolofsson]

Done, see commit f140821