package/ocrad: fix license

ocrad is licensed under GPL-2.0+ since version 0.24, here is an extract
of https://lists.gnu.org/archive/html/bug-ocrad/2014-10/msg00000.html:

"The license has been changed to GPL version 2 or later for better GPL
compatibility. GPLv2 and GPLv2+ programs may use the library now."

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/ocrad/ocrad.mk

@@ -7,7 +7,7 @@
 OCRAD_VERSION = 0.27
 OCRAD_SOURCE = ocrad-$(OCRAD_VERSION).tar.lz
 OCRAD_SITE = $(BR2_GNU_MIRROR)/ocrad
-OCRAD_LICENSE = GPL-3.0+
+OCRAD_LICENSE = GPL-2.0+
 OCRAD_LICENSE_FILES = COPYING
 OCRAD_INSTALL_STAGING = YES