fix rrweb-io/rrweb#395

Author: Yuyz0112

src/snapshot.ts

@@ -309,8 +309,11 @@ function serializeNode(
       }
       if (needBlock) {
         const { width, height } = (n as HTMLElement).getBoundingClientRect();
-        attributes.rr_width = `${width}px`;
-        attributes.rr_height = `${height}px`;
+        attributes = {
+          class: attributes.class,
+          rr_width: `${width}px`,
+          rr_height: `${height}px`,
+        };
       }
       return {
         type: NodeType.Element,

test/__snapshots__/integration.ts.snap

@@ -70,7 +70,7 @@ exports[`[html file]: block-element.html 1`] = `
     <div class=\\"rr-block big\\" style=\\"width: 50px; height: 50px;\\"></div>
     <div>record 2</div>
     <div class=\\"rr-block small\\" style=\\"width: 50px; height: 100px;\\"></div>
-    <div class=\\"rr-block\\" style=\\"height: 200px; width: 100px\\"></div>
+    <div class=\\"rr-block\\" style=\\"width: 100px; height: 200px;\\"></div>
   </body></html>"
 `;