linux-headers: bump 3.18.x version

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
diff --git a/package/linux-headers/Config.in.host b/package/linux-headers/Config.in.host
index 89f7a84..3d77846 100644
--- a/package/linux-headers/Config.in.host
+++ b/package/linux-headers/Config.in.host
@@ -218,7 +218,7 @@
 	default "3.4.113"	if BR2_KERNEL_HEADERS_3_4
 	default "3.10.105"	if BR2_KERNEL_HEADERS_3_10
 	default "3.12.74"	if BR2_KERNEL_HEADERS_3_12
-	default "3.18.53"	if BR2_KERNEL_HEADERS_3_18
+	default "3.18.55"	if BR2_KERNEL_HEADERS_3_18
 	default "3.19.8"	if BR2_KERNEL_HEADERS_3_19
 	default "4.0.9"		if BR2_KERNEL_HEADERS_4_0
 	default "4.1.40"	if BR2_KERNEL_HEADERS_4_1