Add the www-data user group to the skeleton target filesystem

The www-data user is defined in fs/skeleton/etc/passwd, with gid 33. But
gid 33 is not present in the group file.

Signed-off-by: Simon Dawson <spdawson@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

fs/skeleton/etc/group

@@ -7,6 +7,7 @@ tty:x:5:
 disk:x:6:
 wheel:x:10:root
 audio:x:29:
+www-data:x:33:
 utmp:x:43:
 staff:x:50:
 lock:x:54: