scripts: add nconf into gitignore file

scripts/kconfig/nconf is generated by 'make nconfig',
add it into .gitignore.
Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/.gitignore

@@ -17,6 +17,7 @@ gconf.glade.h
 #
 conf
 mconf
+nconf
 qconf
 gconf
 kxgettext