[doc] [2.3.x] Fix JavaWS example to use secure defaults.

There needs to be a better API for creating new WSClient on the fly, but for now this is the simplest(!) thing to do to enable hostname validation.  See the corresponding Scala PR https://github.com/playframework/playframework/pull/3393 for more details.

Also fix lack of intermediate certificate in howsmyssl.com causing the integration test to fail (also filed   https://github.com/jmhodges/howsmyssl/issues/38).
Also remove tabs inside of JavaWS.scala.