remove polyfill

Author: Issa Hanou

_includes/scripts/mathjax.html

@@ -1,12 +1,7 @@
   {%- if site.enable_math -%}
-  <!-- MathJax -->
-  <script type="text/javascript">
-    window.MathJax = {
-      tex: {
-        tags: 'ams'
-      }
-    };
-  </script>
-  <script defer type="text/javascript" id="MathJax-script" src="https://cdn.jsdelivr.net/npm/mathjax@{{ site.mathjax.version }}/es5/tex-mml-chtml.js"></script>
-  <script defer src="https://polyfill.io/v3/polyfill.min.js?features=es6"></script>
+  <!-- KaTeX (client-side) -->
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/katex.min.css">
+  <script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/katex.min.js"></script>
+  <script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/contrib/auto-render.min.js"
+    onload="renderMathInElement(document.body, {delimiters: [{left: '$$', right: '$$', display: true}, {left: '$', right: '$', display: false}], throwOnError: false});"></script>
   {%- endif %}