Raise default memory for VEP

public/biopet-extensions/src/main/scala/nl/lumc/sasc/biopet/extensions/VariantEffectPredictor.scala

@@ -148,6 +148,8 @@ class VariantEffectPredictor(val root: Configurable) extends BiopetCommandLineFu
   // ought to be a flag, but is BUG in VEP; becomes numeric ("1" is true)
   var failed: Option[Int] = config("failed")
 
+  override def defaultCoreMemory = 4.0
+
   override def beforeGraph(): Unit = {
     super.beforeGraph()
     if (!cache && !database) {