linux-headers: bump 3.18.x series

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/linux-headers/Config.in.host

@@ -208,7 +208,7 @@ config BR2_DEFAULT_KERNEL_HEADERS
 	default "3.12.52"	if BR2_KERNEL_HEADERS_3_12
 	default "3.14.59"	if BR2_KERNEL_HEADERS_3_14
 	default "3.17.8"	if BR2_KERNEL_HEADERS_3_17
-	default "3.18.25"	if BR2_KERNEL_HEADERS_3_18
+	default "3.18.26"	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 "4.1.16"	if BR2_KERNEL_HEADERS_4_1