Replace spray-json fork with something for longer term

[ekrich]

sconfig uses a JSON library to compare the JSON parsing to the internal parser as a sanity check - this could be replaced potentially with a good JSON test lib.

The original lightbend/config uses "net.liftweb" %% "lift-json" % "3.3.0" % Test https://www.liftweb.net/ but this was not cross platform.

This was replaced by https://github.com/jodersky/spray-json to get a cross platform version of
https://github.com/spray/spray-json The code has been merged upstream but it doesn't seem to have a cross version as the master branch is behind and not using current Scala Native versions for example.

It is unclear the path forward but it seems only JVM is involved using TestUtils and JsonTest so right now now cross platform tests are involved.