upgrade docker plugin to docker 1.12

.drone.yml

@@ -13,20 +13,10 @@ pipeline:
       - go test -cover -coverprofile=coverage.out
       - go build -ldflags "-s -w -X main.build=$DRONE_BUILD_NUMBER" -a -tags netgo
 
-  latest:
+  publish:
     image: plugins/docker
     repo: plugins/docker
-    tags: [ "latest", "1.2", "1" ]
+    tags: [ "latest", "1.3", "1" ]
     when:
       branch: master
       event: push
-
-plugin:
-  name: Docker
-  desc: Build and publish images to a Docker registry
-  type: publish
-  image: plugins/docker
-  labels:
-    - docker
-    - image
-    - container