This change stops using the short-hand "!Ref" YAML syntax. The Golang
marshaler encodes it with quotes and, apparently, has no way to suppress
this behavior; this isn't surprising, since the YAML parser we're using
admits it doesn't support this aspect of the YAML spec fully. But that's
okay, the long-hand syntax works just fine, and has the added benefit
that we don't need to special case the logig for JSON versus YAML.