Update WPT tests.

Author: fred-wang

index.html

@@ -2448,7 +2448,7 @@ <h5>Fraction with nonzero line thickness</h5>
               <a>fraction line thickness</a>.
             </p>
           </section>
-          <section>
+          <section id="fraction-with-zero-line-thickness">
             <h5>Fraction with zero line thickness</h5>
             <p>
               If the <a>fraction line thickness</a> is zero,