fix an error in the nginx rewrite (#2634)

Author: ElliotFriend

nginx/includes/redirects.conf

@@ -118,7 +118,7 @@ rewrite ^/docs/learn/networks$ "/docs/networks" permanent;
 rewrite ^/docs/learn/fundamentals/networks$ "/docs/networks" permanent;
 
 # Meetings: old slug formats
-rewrite ^/meeting-notes/([0-9]{4})-([0-9]{2})-([0-9]{2})/?$ "/meetings/$1/$2/$3" permanent;
+rewrite ^/meeting-notes/(\d\d\d\d)-(\d\d)-(\d\d)/?$ "/meetings/$1/$2/$3" permanent;
 rewrite ^/meeting-notes(.*)$ "/meetings$1" permanent;
 
 # Move some categories around