logrotate: use specific log file paths

This avoids ending up with the glob path in the logrotate state file
when nothing matches the glob pattern.

etc/logrotate.d/letsencrypt

@@ -1,3 +1,3 @@
-/var/log/letsencrypt/*.log {
+/var/log/letsencrypt/letsencrypt.log {
     missingok
 }

etc/logrotate.d/nginx

@@ -1,4 +1,4 @@
-/var/log/nginx/*log {
+/var/log/nginx/access.log /var/log/nginx/error.log {
     missingok
     create 600 root root
     sharedscripts