Added API version negotiation to group.go (#28)

* Update lazytainer.go

Negotiate docker API version to prevent "client version is too new" error

* Update group.go

negotiate docker API version

src/group.go

@@ -74,6 +74,7 @@ func (lg LazyGroup) MainLoop() {
 func (lg LazyGroup) getContainers() []types.Container {
 	dockerClient, err := client.NewClientWithOpts(client.FromEnv)
 	check(err)
+	dockerClient.NegotiateAPIVersion(context.Background())
 	filter := filters.NewArgs(filters.Arg("label", "lazytainer.group="+lg.groupName))
 	containers, err := dockerClient.ContainerList(context.Background(), types.ContainerListOptions{All: true, Filters: filter})
 	check(err)
@@ -85,6 +86,7 @@ func (lg LazyGroup) stopContainers() {
 	debugLogger.Println("stopping container(s)")
 	dockerClient, err := client.NewClientWithOpts(client.FromEnv)
 	check(err)
+	dockerClient.NegotiateAPIVersion(context.Background())
 	for _, c := range lg.getContainers() {
 		if lg.sleepMethod == "stop" || lg.sleepMethod == "" {
 			if err := dockerClient.ContainerStop(context.Background(), c.ID, container.StopOptions{}); err != nil {
@@ -106,6 +108,7 @@ func (lg LazyGroup) startContainers() {
 	debugLogger.Println("starting container(s)")
 	dockerClient, err := client.NewClientWithOpts(client.FromEnv)
 	check(err)
+	dockerClient.NegotiateAPIVersion(context.Background())
 	for _, c := range lg.getContainers() {
 		if lg.sleepMethod == "stop" || lg.sleepMethod == "" {
 			if err := dockerClient.ContainerStart(context.Background(), c.ID, types.ContainerStartOptions{}); err != nil {