Prettify generated csvw output

[mchlrch]

The generated code looks odd due to the line separator ',' not being added at the end of line.
(source https://zulip.zazuko.com/#narrow/stream/34-rdf-workbench/topic/rdf-mapping-dsl/near/58668)

"dialect": {
                "delimiter": ","
                ,"commentPrefix": "#"
                ,"doubleQuote": true
                ,"encoding": "utf-8"
                ,"header": true
                ,"headerRowCount": "1"
                ,"lineTerminators": "\r\n"
                ,"quoteChar": "\""
                ,"skipBlankRows": false
                ,"skipInitialSpace": false
                ,"trim": false
            }
// ...