mod_md.xml: fix typo

                <li>All request to the <code>http:</code> resources are redirected to the

                    same url with the <code>https:</code> scheme using the <code>301</code>

                status code. This tells clients that this is intended to be forever and

                the should update any links they have accodingly.

                the should update any links they have accordingly.

                </li>

                <li>All answers to <code>https:</code> requests will carry the header

                    <code>Strict-Transport-Security</code> with a life time of half a year.