update footnotes test output to fix test fail

Author: shenxianpeng

tests/fixtures/test_GFM_footnotes.html

@@ -1,8 +1,8 @@
-<p>a statement<sup class="footnote-ref"><a href="#fn-1" id="fnref-1" data-footnote-ref>1</a></sup></p>
-<section class="footnotes" data-footnotes>
+<p>a statement<sup><a href="#fn-1" id="fnref-1" rel="nofollow">1</a></sup></p>
+<section>
 <ol>
 <li id="fn-1">
-<p>this is true <a href="#fnref-1" class="footnote-backref" data-footnote-backref data-footnote-backref-idx="1" aria-label="Back to reference 1">↩</a></p>
+<p>this is true <a href="#fnref-1" rel="nofollow">↩</a></p>
 </li>
 </ol>
 </section>