combo增加blur事件

src/less/base/single/input/checkbox.less

@@ -13,8 +13,9 @@
       border: 2px solid transparent;
       border-top: 0;
       border-left: 0;
-      width: 4px;
+      width: 6px;
-      height: 8px;
+      height: 9px;
+      .box-sizing(border-box);
       .transform(rotate(45deg) scale(1) translate(-50%, -50%));
       content: '';
     }