a spy method should be enumerable

Author: koba04

packages/enzyme/src/Utils.js

@@ -254,7 +254,7 @@ export function spyMethod(instance, methodName) {
   }
   Object.defineProperty(instance, methodName, {
     configurable: true,
-    enumerable: false,
+    enumerable: !descriptor || !!descriptor.enumerable,
     value(...args) {
       const result = originalMethod.apply(this, args);
       lastReturnValue = result;