style(header): fix `notify` icon color in dark

修复暗色header中的通知图标的颜色问题

src/layouts/default/header/index.less

@@ -181,6 +181,12 @@
           font-size: 16px !important;
         }
 
+        .ant-badge {
+          span {
+            color: @white;
+          }
+        }
+
         &:hover {
           background-color: @header-dark-bg-hover-color;
         }