package/bwm-ng: license is GPL-2.0+

The source files contain the "(at your option) any later version" text, so
change the licese to GPL-2.0+.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit f58ea370da70a3bbda174f77d3094975bb142161)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/bwm-ng/bwm-ng.mk

@@ -7,7 +7,7 @@
 BWM_NG_VERSION = f54b3fad2c80bfe63f920c9b5e7c1d80389c57ef
 BWM_NG_SITE = $(call github,vgropp,bwm-ng,$(BWM_NG_VERSION))
 BWM_NG_CONF_OPTS = --with-procnetdev --with-diskstats
-BWM_NG_LICENSE = GPL-2.0
+BWM_NG_LICENSE = GPL-2.0+
 BWM_NG_LICENSE_FILES = COPYING
 BWM_NG_AUTORECONF = YES