TestSelector -> SuiteSelector due to exception

```
java.lang.ClassCastException: sbt.testing.SuiteSelector cannot be cast to sbt.testing.TestSelector
	at ca.seibelnet.TestGroupXmlWriter$$anonfun$1$$anonfun$apply$1.apply(TestGroupXmlWriter.scala:54)
	at ca.seibelnet.TestGroupXmlWriter$$anonfun$1$$anonfun$apply$1.apply(TestGroupXmlWriter.scala:53)
	at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
```