Use 'throw new NotImplementedError()' instead of '???'

Author: techncl

csv-validator-core/src/test/scala/uk/gov/nationalarchives/csv/validator/api/CsvValidatorSpec.scala

@@ -64,7 +64,7 @@ class CsvValidatorSpec extends Specification with TestResources {
     val callback = new ProgressCallback {
       var processed = -1
       var total = -2
-      override def update(complete: Percentage): Unit = ???
+      override def update(complete: Percentage): Unit = throw new NotImplementedError()
 
       override def update(_total: Int, _processed: Int): Unit = {
         total = _total