correct list-style of groups

src/styles/components/select.less

@@ -191,6 +191,10 @@
     &-multiple .@{css-prefix}tag{
         margin: 3px 4px 2px 0;
     }
+
+    &-dropdown-list {
+        list-style: none;
+    }
 }
 
 .select-item(@select-prefix-cls, @select-item-prefix-cls);
@@ -244,4 +248,4 @@
             .active-error;
         }
     }
-}
+}