fix(modal): 取消全屏功能后关闭图标颜色异常 (#1240)

Co-authored-by: liushiman <smliu@gk-estor.com>

src/components/Modal/src/components/ModalClose.vue

@@ -97,7 +97,7 @@
       }
     }
 
-    & span:nth-child(2) {
+    & span:last-child {
       &:hover {
         color: @error-color;
       }