fix NPM mod syntax error (#412)

* fix syntax error

* add conditional semi colon

Co-authored-by: GilbN <24592972+GilbN@users.noreply.github.com>
Co-authored-by: GilbN <gilberg@gmail.com>

docker-mods/nginx-proxy-manager/root/etc/cont-init.d/98-themepark

@@ -4,7 +4,7 @@ echo '--------------------------------------'
 echo '| Nginx Proxy Manager theme.park Mod |' 
 echo '--------------------------------------'
 
-if [ -d "/app/frontend" ] then
+if [[ -d "/app/frontend" ]]; then
     APP_FILEPATH='/app/frontend/' # jc21/nginx-proxy-manager
 else
     APP_FILEPATH='/opt/nginx-proxy-manager/frontend/' # jlesage/nginx-proxy-manager