test: update back-top snap

Author: Amour1688

components/back-top/__tests__/__snapshots__/demo.test.js.snap

@@ -2,18 +2,10 @@
 
 exports[`renders ./antdv-demo/docs/back-top/demo/basic.md correctly 1`] = `
 <div>
-  <!---->
-  Scroll down to see the bottom-right
-  <strong style="color: rgba(64, 64, 64, 0.6);"> gray </strong>
-  button.
-</div>
+  <!----> Scroll down to see the bottom-right <strong style="color: rgba(64, 64, 64, 0.6);"> gray </strong> button. </div>
 `;
 
 exports[`renders ./antdv-demo/docs/back-top/demo/custom.md correctly 1`] = `
 <div id="components-back-top-demo-custom">
-  <!---->
-  Scroll down to see the bottom-right
-  <strong style="color: rgb(16, 136, 233);"> blue </strong>
-  button.
-</div>
+  <!----> Scroll down to see the bottom-right <strong style="color: rgb(16, 136, 233);"> blue </strong> button. </div>
 `;