Use PyNUTClient from PyPI

--- nut-2.8.1/scripts/python/app/NUT-Monitor-py3qt5.in.orig
+++ nut-2.8.1/scripts/python/app/NUT-Monitor-py3qt5.in
@@ -46,7 +46,7 @@
 import configparser
 import locale
 import gettext
-import PyNUT
+import PyNUTClient as PyNUT
 
 
 class interface :