# edit file
sudo vi /etc/apache2/sites-available/000-default-le-ssl.conf
# in "VirtualHost" fragment
RewriteEngine on
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP:X-Forwarded-Proto} !https
RewriteRule ^/(.*) https://%{HTTP_HOST}/$1 [NC,R=301,L]