Improve Dropdown Button examples

components/dropdown/demo/dropdown-button.md

@@ -6,8 +6,7 @@ title: 带下拉框的按钮
 左边是按钮，右边是额外的相关功能菜单。
 
 ````jsx
-import { Menu, Dropdown } from 'antd';
-const DropdownButton = Dropdown.Button;
+import { Menu, Dropdown, Button, Icon } from 'antd';
 
 function handleButtonClick(e) {
   console.log('click left button', e);
@@ -26,8 +25,15 @@ const menu = (
 );
 
 ReactDOM.render(
-  <DropdownButton onClick={handleButtonClick} overlay={menu} type="primary">
+  <div>
+    <Dropdown.Button onClick={handleButtonClick} overlay={menu} type="ghost">
       某功能按钮
-  </DropdownButton>
+    </Dropdown.Button>
+    <Dropdown overlay={menu}>
+      <Button type="ghost" style={{ marginLeft: 8 }}>
+        按钮 <Icon type="down" />
+      </Button>
+    </Dropdown>
+  </div>
 , mountNode);
 ````

components/dropdown/style/index.less

@@ -17,7 +17,7 @@
     position: relative;
 
     .ant-btn > .@{iconfont-css-prefix}-down {
-      .iconfont-size-under-12px(10px);
+      .iconfont-size-under-12px(9px);
     }
 
     .anticon-down:before {
@@ -110,7 +110,7 @@
       content: "\e600";
       right: 15px;
       color: #999;
-      .iconfont-size-under-12px(8px);
+      .iconfont-size-under-12px(9px);
     }
 
     &-submenu-vertical {
@@ -157,7 +157,7 @@
 .@{dropdown-prefix-cls}-link {
   font-size: 12px;
   .anticon-down {
-    .iconfont-size-under-12px(8px);
+    .iconfont-size-under-12px(9px);
     font-weight: bold;
   }
 }
@@ -167,6 +167,10 @@
     padding-right: 7px;
   }
   .anticon-down {
-    .iconfont-size-under-12px(10px);
+    .iconfont-size-under-12px(9px);
   }
 }
+
+.ant-btn .anticon-down {
+  .iconfont-size-under-12px(9px);
+}