Makefile: fix typo created when spliting the install targets

Makefile

@@ -359,7 +359,7 @@ install-networkmanager:
 	install network/{qubes-nmhook,30-qubes-external-ip} $(DESTDIR)/etc/NetworkManager/dispatcher.d/
 
 	install -d $(DESTDIR)/usr/lib/NetworkManager/conf.d
-	install -m 0644 network/nm-30-qubes.conf $(DESTDIR)/usr/lib/NetworkManager/conf.d/30
+	install -m 0644 network/nm-30-qubes.conf $(DESTDIR)/usr/lib/NetworkManager/conf.d/30-qubes.conf
 
 	install -d $(DESTDIR)/etc/xdg/autostart
 	install -m 0755 network/show-hide-nm-applet.sh $(DESTDIR)$(LIBDIR)/qubes/