Add missing < in opening <a> tag

examples/classic-slides/index.html

@@ -338,7 +338,7 @@
         <h1><a href="http://docs.mathjax.org/en/latest/start.html">MathJax.js</a></h1>
         <p>Use \(\LaTeX\), MathML or AsciiMath to properly show mathematical formula.</p>
         <div class="notes">
-          Mermaid.js, likewise in a href="https://github.com/impress/impress.js/tree/master/extras">extras/</a>
+          Mermaid.js, likewise in <a href="https://github.com/impress/impress.js/tree/master/extras">extras/</a>
            directory, draws SVG diagrams from a MarkDown-like syntax. To learn
           more about it <a href="http://knsv.github.io/mermaid/index.html#usage">read the fine manual</a>.
         </div>