JsonLine should handle empty lines
Currently it fails while parsing
Default behaviour is now to keep failing on empty lines, thus preserving previous behavior
Merge branch 'develop' of https://github.com/twitter/scalding into develop

Conflicts:
	scalding-json/src/main/scala/com/twitter/scalding/JsonLine.scala
	scalding-json/src/test/scala/com/twitter/scalding/JsonLineTest.scala
Merge pull request #966 from mariussoutier/develop

JsonLine should handle empty lines