Fix the Mastodon link

content/about.html

@@ -28,7 +28,7 @@
 
             <h3>Contact</h3>
             <ul>
-                <li>EMail: <i>{{ email_user }} ["a" with a weird circle] {{ email_domain }}</i> (<a href="{{ email_gpg_url}}">GPG</a>)</li>
+                <li>EMail: <i>{{ email_user }} ["a" with a weird circle] {{ email_domain }}</i> (<a href="https://{{ email_gpg_url}}">GPG</a>)</li>
             </ul>
 
             <h3>About This Page</h3>