trifold add right binding

not sure if this is correct for ever flyer

models/printer.go

@@ -15,7 +15,7 @@ const (
 	LongEdge      PrintOption = ""
 	ShortEdge     PrintOption = "-o Binding=TopBinding"
 	CreateBooklet PrintOption = "-o Combination=Booklet -o PageSize=A5"
-	TriFold       PrintOption = "-o Fold=TriFold"
+	TriFold       PrintOption = "-o Fold=TriFold -o Binding=RightBinding"
 )
 
 type PrintJob struct {