update locale demo

components/date-picker/demo/locale.md

@@ -2,30 +2,24 @@
 
 - order: 10
 
-通过 `locale` 配置时区、语言等, 默认支持 en_US, zh_CN
+通过 `locale` 配置时区、语言等, 默认支持 `en_US`，`zh_CN`。
 
 ---
 
 ````jsx
 import { DatePicker } from 'antd';
 import enUS from 'antd/lib/date-picker/locale/en_US';
-import assign from 'object-assign';
 
 const App = React.createClass({
-  getInitialState() {
-    return {
-      locale: assign({}, enUS, {
-        timezoneOffset: 0 * 60,
-        firstDayOfWeek: 0,
-        minimalDaysInFirstWeek: 1,
-      })
-    };
-  },
   render() {
-    return <DatePicker locale={this.state.locale} />;
+    const customLocale = {
+      timezoneOffset: 0 * 60,
+      firstDayOfWeek: 0,
+      minimalDaysInFirstWeek: 1,
+    };
+    return <DatePicker locale={{ ...enUS, ...customLocale }} />;
   }
 });
 
 ReactDOM.render(<App />, mountNode);
 ````
-