Update index.html

Author: coding-horror

index.html

@@ -112,7 +112,7 @@ <h3>
                     The CommonMark specification.
                 </p>
                 <h3>
-                    <a href="https://code.commonmark.org/">code.commonmark.org</a>
+                    <a href="https://github.com/commonmark">code.commonmark.org</a>
                 </h3>
                 <p>
                     Reference implementation and validation test suite on GitHub.