Update style.md

usage of Arrow function

docs/style.md

@@ -260,9 +260,14 @@ const nodes = Array.from(foo);
 });
 
 // good
-[1, 2, 3].map((x) => {
+[1, 2, 3].map(x => {
   return x * x;
 });
+
+// with more than one argument
+[1, 2, 3].map((x,i) => {
+  return x * i;
+});
 ```
 
 箭头函数取代`Function.prototype.bind`，不应再用self/\_this/that绑定 this。