libnotify: set GNOME_COMPRESS_TYPE to bz2

libnotify: set GNOME_COMPRESS_TYPE to bz2

Fixed do_fetch error:
WARNING: Failed to fetch URL http://ftp.gnome.org/pub/GNOME/sources/libnotify/0.6/libnotify-0.6.0.tar.xz;name=archive, attempting MIRRORS if available
ERROR: Fetcher failure: Fetch command failed with exit code 8, output:
http://ftp.gnome.org/pub/GNOME/sources/libnotify/0.6/libnotify-0.6.0.tar.xz:
2015-08-25 02:31:32 ERROR 404: Not Found.

There are .tar.gz and .bz2, but no .tar.xz.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>