update 骨架屏组件居中问题

src/packages/skeleton/skeleton.scss

@@ -35,12 +35,14 @@
     display: flex;
     flex-direction: column;
     justify-content: center;
+    align-items: center;
 }
 
 .vue-skeleton-row {
     display: flex;
     flex-direction: row;
     align-items: center;
+    justify-content: center;
 }
 
 .vue-skeleton-square-wrap {