zxing: add version of the Apache license

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/zxing/zxing.mk

@@ -6,7 +6,7 @@
 ZXING_VERSION = 2.0
 ZXING_SITE = http://zxing.googlecode.com/files
 ZXING_SOURCE = ZXing-$(ZXING_VERSION).zip
-ZXING_LICENSE = Apache
+ZXING_LICENSE = Apache v2.0
 ZXING_LICENSE_FILES = COPYING
 ZXING_INSTALL_STAGING = YES