Duplicated key in YAML

[junjun-zhang]

Although it does not cause a failure, duplicated key in YAML should probably be avoid:
https://github.com/ICGC-TCGA-PanCancer/CGP-Somatic-Docker/blob/develop/Dockstore.cwl#L10-L14

Encounter warning message when testing this workflow for GA4GH dream challenge.

[denis-yuen]

What is giving a warning?

I'm far from an expert on this kind of metadata, but my impression was that metadata terms can be repeated, in this case to denote multiple contributors

Properties may be repeated.

http://www.dublincore.org/documents/dc-xml-guidelines/