in serialization rename op to term

app/models/logic/n_ary_operator.rb

@@ -8,7 +8,7 @@ class Logic::NAryOperator < Logic::Term
 
   def to_h
     {
-      "op" => self.class.name,
+      "term" => self.class.name,
       "operands" => @operands.map(&:to_h),
       "id" => @id
     }