nixos/zoneminder: Fix nginx config check

NixOS wouldn't build because the nginx config checker fails.

Location without a trailing slash "could allow an attacker to read file
stored outside the target folder.", source:
https://github.com/yandex/gixy/blob/master/docs/en/plugins/aliastraversal.md

Shouldn't change the behaviour according to
https://serverfault.com/questions/607615/using-trailing-slashes-in-nginx-configuration/607731#607731

nixos/modules/services/misc/zoneminder.nix

@@ -256,7 +256,7 @@ in {
                   fastcgi_pass ${fcgi.socketType}:${fcgi.socketAddress};
                 }
 
-                location /cache {
+                location /cache/ {
                   alias /var/cache/${dirName};
                 }