Fix exitcode on version command

biopet-framework/src/main/scala/nl/lumc/sasc/biopet/extensions/seqtk/Seqtk.scala

@@ -15,4 +15,5 @@ abstract class Seqtk extends BiopetCommandLineFunction {
   executable = config("exe", default = "seqtk", submodule = "seqtk")
   override def versionCommand = executable
   override val versionRegex = """Version: (.*)""".r
+  override val versionExitcode = List(0, 1)
 }