Fix apostrophe formatting in theorem HTML

Author: douden

tests/test_html/theorem/_theorems_with_number.html

@@ -1,6 +1,6 @@
 <div class="proof theorem admonition" id="theorem-one">
 <p class="admonition-title"><span class="caption-number">Theorem 1 </span> (Important Theorem)</p>
 <section class="theorem-content" id="proof-content">
-<p>It's true.</p>
+<p>It’s true.</p>
 </section>
 </div>