fix ruamel.yaml on 0.14.X for now
fix ruamel.yaml on 0.14.X for now

Thank you for using ruamel.yaml. 

There will be API changes in the 0.15+ versions, that might lead to warnings that 
your users could see. 
Therefore please release a version of your package with this change, so that it will not 
automatically take the latest ruamel.yaml release.
lsst-sqre/ltd-mason,lsst-sqre/ltd-mason