update the docker plugin to use the default volume as the graph path

.drone.yml

@@ -9,7 +9,7 @@ pipeline:
       - go test -cover -coverprofile=coverage.out
       - go build -ldflags "-s -w -X main.build=$DRONE_BUILD_NUMBER"
   docker:
-    storage_driver: overlay
+    storage_driver: vfs
     repo: plugins/docker
     tag: [ "latest", "1.0", "1" ]
     when:

.drone.yml.sig

@@ -1 +1 @@
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+eyJhbGciOiJIUzI1NiJ9.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.F6oON9CzmytJ6osktjK8bLDkJLpepNb5dvCUPbjgr_U

Dockerfile

@@ -6,4 +6,4 @@ FROM docker:1.11-dind
 
 ADD drone-docker /bin/
 
-ENTRYPOINT ["/bin/drone-docker"]
+ENTRYPOINT [ "/usr/local/bin/dockerd-entrypoint.sh", "/bin/drone-docker" ]

main.go

@@ -50,7 +50,7 @@ func main() {
 		cli.StringFlag{
 			Name:   "daemon.storage-path",
 			Usage:  "docker daemon storage path",
-			Value:  "/tmp/docker",
+			Value:  "/var/lib/docker",
 			EnvVar: "PLUGIN_STORAGE_PATH",
 		},
 		cli.StringFlag{