Merge branch 'fix-combinevariants' into 'develop'

Fix for issue #167

See merge request !172

public/biopet-framework/src/main/scala/nl/lumc/sasc/biopet/extensions/gatk/CombineVariants.scala

@@ -46,6 +46,7 @@ class CombineVariants(val root: Configurable) extends Gatk {
   }
 
   override def beforeGraph: Unit = {
+    super.beforeGraph
     genotypeMergeOptions match {
       case Some("UNIQUIFY") | Some("PRIORITIZE") | Some("UNSORTED") | Some("REQUIRE_UNIQUE") | None =>
       case _ => throw new IllegalArgumentException("Wrong option for genotypeMergeOptions")