fix http references, convert to https

index.html

@@ -97,7 +97,7 @@ <h2>
                     <a id="how" class="anchor" href="#how"></a>How can I help?
                 </h2>
 
-                <p>Exercise our <a href="http://code.commonmark.org/">reference implementations</a>, or <a href="https://github.com/jgm/CommonMark/wiki/List-of-CommonMark-Implementations">find a community implementation</a> in your preferred environment or language. Provide <a href="https://talk.commonmark.org"></a>feedback!</p>
+                <p>Exercise our <a href="https://code.commonmark.org/">reference implementations</a>, or <a href="https://github.com/jgm/CommonMark/wiki/List-of-CommonMark-Implementations">find a community implementation</a> in your preferred environment or language. Provide <a href="https://talk.commonmark.org"></a>feedback!</p>
 
                 <p>If a CommonMark implementation does not already exist in your preferred environment or language, try <strong>implementing your own CommonMark parser</strong>. One of our major goals is to <a href="https://spec.commonmark.org/">strongly specify Markdown</a>, and to eliminate the many old inconsistencies and ambiguities that made using Markdown so difficult. Did we succeed?</p>
 
@@ -112,7 +112,7 @@ <h3>
                     The CommonMark specification.
                 </p>
                 <h3>
-                    <a href="http://code.commonmark.org/">code.commonmark.org</a>
+                    <a href="https://code.commonmark.org/">code.commonmark.org</a>
                 </h3>
                 <p>
                     Reference implementation and validation test suite on GitHub.