fix(tag): fix tag link style

components/tag/demo/basic.md

@@ -17,6 +17,6 @@ ReactDOM.render(<div>
   <Tag>标签一</Tag>
   <Tag>标签二</Tag>
   <Tag closable onClose={onClose}>标签三</Tag>
-  <a href="https://www.alipay.com/" target="_blank"><Tag>标签四（链接）</Tag></a>
+  <Tag><a href="https://www.alipay.com/" target="_blank">标签四（链接）</a></Tag>
 </div>, mountNode);
 ````

style/components/tag.less

@@ -27,6 +27,14 @@
     color: @text-color;
   }
 
+  &-text {
+    a:first-child:last-child {
+      display: block;
+      margin: 0 -8px;
+      padding: 0 8px;
+    }
+  }
+
   .anticon-cross {
     .iconfont-size-under-12px(10px);
     cursor: pointer;