Adjust prompt for the post-build scripts option

Since the post-image config option uses the plural for "Custom
scripts", do the same for the post-build config option, for
consistency.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

system/Config.in

@@ -261,7 +261,7 @@ config BR2_ROOTFS_OVERLAY
 	  ~ and .git, .svn and .hg directories.
 
 config BR2_ROOTFS_POST_BUILD_SCRIPT
-	string "Custom script to run before creating filesystem images"
+	string "Custom scripts to run before creating filesystem images"
 	default ""
 	help
 	  Specify a space-separated list of scripts to be run after the build