audiofile: fix license

Somehow this didn't get committed in 1eb9845ad6 (add license information)

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/audiofile/audiofile.mk

@@ -8,7 +8,7 @@ AUDIOFILE_VERSION = 0.3.4
 AUDIOFILE_SITE = http://audiofile.68k.org
 AUDIOFILE_INSTALL_STAGING = YES
 AUDIOFILE_CONF_ENV = ac_cv_prog_cc_c99='-std=gnu99'
-AUDIOFILE_LICENSE = GPLv2 LGPLv2
+AUDIOFILE_LICENSE = GPLv2+ LGPLv2+
 AUDIOFILE_LICENSE_FILES = COPYING COPYING.GPL
 
 # Useless and needs alsa-lib