grep: bump version to 2.18

Signed-off-by: Tamás Lévai <levai.tamas@t-online.hu>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/grep/grep.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-GREP_VERSION = 2.16
+GREP_VERSION = 2.18
 GREP_SITE = $(BR2_GNU_MIRROR)/grep
 GREP_SOURCE = grep-$(GREP_VERSION).tar.xz
 GREP_LICENSE = GPLv3+