Update sdo-periodical-examples.txt
Update sdo-periodical-examples.txt

Removed erroneous declaration of schema: prefix in JSON-LD example
Fix to issue #2172
schemaorg/schemaorg,vholland/schemaorg,vholland/schemaorg,vholland/schemaorg,schemaorg/schemaorg,vholland/schemaorg,schemaorg/schemaorg,schemaorg/schemaorg,schemaorg/schemaorg