docker-engine: security bump to version 1.12.6

Fixes runC privilege escalation (CVE-2016-9962).

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/docker-engine/docker-engine.hash

@@ -1,2 +1,2 @@
 # Locally calculated
-sha256 81b337368efafb631a75f6ad5469413fd5828ce672592c374adf894dc05abd38  docker-engine-v1.12.5.tar.gz
+sha256 0413f3513c2a6842ed9cf837154c8a722e9b34cb36b33430348489baa183707e  docker-engine-v1.12.6.tar.gz

package/docker-engine/docker-engine.mk

@@ -4,8 +4,8 @@
 #
 ################################################################################
 
-DOCKER_ENGINE_VERSION = v1.12.5
-DOCKER_ENGINE_COMMIT = 7392c3b0ce0f9d3e918a321c66668c5d1ef4f689
+DOCKER_ENGINE_VERSION = v1.12.6
+DOCKER_ENGINE_COMMIT = 78d18021ecba00c00730dec9d56de6896f9e708d
 DOCKER_ENGINE_SITE = $(call github,docker,docker,$(DOCKER_ENGINE_VERSION))
 
 DOCKER_ENGINE_LICENSE = Apache-2.0