Results 3 issues of kiris

Correspond to Scala 2.12.4. I'm resolved compile errors ``` $ sbt compile [error] /Users/kiris/local/src/cronish/src/main/scala/dsl.scala:84: recursive method monthnames needs result type [error] def monthValue = (monthnames).mkString("|").r ^^ { [error] /Users/kiris/local/src/cronish/src/main/scala/dsl.scala:217: value...

I try to parse big table element with ContentExtractors.table. but, buildRow and buildTable method is not tail recursion. Thereby ContentExtractors.table function throwed StackOverflowError. that failed to parse URL: http://www.tipness.co.jp/schedule/SHP063/month

Default field values is great to express the optional fields. but, other parse error in hiding until. I want don't use Default field values by other parse error case. https://github.com/aparo/play-json-extra/blob/43b2eb7765d467b7310d8f48da4ff6d6b9434d5c/play-json-extra/shared/src/main/scala/play/json/extra/extra.scala#L262