Update instructions to fix the automatic upgrade

wiki/src/home.html

@@ -34,7 +34,7 @@ to the latest version of Tails.</p>
     </li>
     <li>
       <p>In a terminal, execute the following command:</p>
-      <pre><code>torsocks curl --silent https://letsencrypt.org/certs/lets-encrypt-r3.pem \
+      <pre><code>torsocks curl --silent https://letsencrypt.org/certs/isrg-root-x1-cross-signed.pem \
 | sudo tee --append /usr/local/etc/ssl/certs/tails.boum.org-CA.pem \
 &amp;&amp; systemctl --user restart tails-upgrade-frontend
 </code></pre>