package/docker-engine: bump to v1.12.0

Bump docker-engine to the latest stable v1.12.0 from v1.12.0-rc3.

Signed-off-by: Christian Stewart <christian@paral.in>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit f892015d78eb0f2cc7ddd754beabcf41bfa6da6b)

package/docker-engine/docker-engine.hash

@@ -1,2 +1,2 @@
 # Locally calculated
-sha256 bc256d2a348efbf236eab991254c925fa1917dd1e29cb40586f1696f4e24852e  docker-engine-v1.12.0-rc4.tar.gz
+sha256 f8139acba98248eb1fdb0b6d94efee89b876f9a50d00e263dc144fd2b0c372d4  docker-engine-v1.12.0.tar.gz

package/docker-engine/docker-engine.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-DOCKER_ENGINE_VERSION = v1.12.0-rc4
+DOCKER_ENGINE_VERSION = v1.12.0
 DOCKER_ENGINE_SITE = $(call github,docker,docker,$(DOCKER_ENGINE_VERSION))
 
 DOCKER_ENGINE_LICENSE = Apache-2.0