Update default prefixCls in README.md

Author: afc163

README.md

@@ -48,7 +48,7 @@ Please note that **onChange** API
 
 | Property     | Type                                                           | Default      | Description                        |
 | --------- | --------- | --------- | --------- |
-| prefixCls    | string                                                         | @rc-component/segmented | prefixCls of this component |
+| prefixCls    | string                                                         | `rc-segmented` | prefixCls of this component |
 | className    | string                                                         | ''           | additional class name of segmented |
 | style        | React.CSSProperties                                            |              | style properties of segmented      |
 | options      | Array<string \| number \| [SegmentedOption](#SegmentedOption)> | []           | options for choices                |