docs(symbol): edit symbol/Symbol.instanceOf

docs/symbol.md

@@ -492,6 +492,13 @@ class Even {
   }
 }
 
+// 等同于
+const Even = {
+  [Symbol.hasInstance](obj) {
+    return Number(obj) % 2 === 0;
+  }
+};
+
 1 instanceof Even // false
 2 instanceof Even // true
 12345 instanceof Even // false