Install certbot from repo (#38)

lib/os/class.ISPConfigDebianOS.inc.php

@@ -932,13 +932,7 @@ mailman-unsubscribe:  "|/var/lib/mailman/mail/mailman unsubscribe mailman"';
 
 		if (ISPConfig::wantsCertbot()) {
 			ISPConfigLog::info('Installing Certbot (Let\'s Encrypt).', true);
-			$cmd = 'cd /usr/local/bin ; wget https://dl.eff.org/certbot-auto ; chmod a+x certbot-auto ; ./certbot-auto --install-only';
-			$result = $this->exec($cmd);
-			if($result === false) {
-				ISPConfigLog::warn('Installation of Certbot (Let\'s Encrypt) failed.', true);
-			} else {
-				ISPConfigLog::info('Certbot installed.', true);
-			}
+			$this->installPackages('certbot');
 		} else {
 			ISPConfigLog::info('Installing acme.sh (Let\'s Encrypt).', true);
 			$cmd = 'cd /tmp ; wget -O -  https://get.acme.sh 2>/dev/null | sh 2>/dev/null';