chore: prettier source code

src/dropdown-menu/index.js

@@ -77,7 +77,7 @@ export default createComponent({
     },
 
     onClickOutside() {
-      this.children.forEach(item => {
+      this.children.forEach((item) => {
         item.toggle(false);
       });
     },

src/dropdown-menu/test/index.spec.js

@@ -213,7 +213,7 @@ test('change event', async () => {
   expect(onChange).toHaveBeenCalledTimes(1);
 });
 
-test('toggle method', async done => {
+test('toggle method', async (done) => {
   const wrapper = mount({
     template: `
       <van-dropdown-menu>