Remove deprecated supervisor spec

[rodrigues]

Remove the deprecations listed below.

Elixir ~> 1.7, already specified in mix.exs as dependency, already includes the child specs: elixir-lang/elixir@43f80d3

warning: Supervisor.Spec.supervise/2 is deprecated. Use the new child specifications outlined in the Supervisor module instead
  lib/kaffe/consumer_group/group_member_supervisor.ex:63: Kaffe.GroupMemberSupervisor.init/1

warning: Supervisor.Spec.supervise/2 is deprecated. Use the new child specifications outlined in the Supervisor module instead
  lib/kaffe/consumer_group/worker/worker_supervisor.ex:36: Kaffe.WorkerSupervisor.init/1

warning: Supervisor.Spec.supervisor/2 is deprecated. Use the new child specifications outlined in the Supervisor module instead
  lib/kaffe/consumer_group/group_member_supervisor.ex:35: Kaffe.GroupMemberSupervisor.start_worker_supervisor/2

warning: Supervisor.Spec.worker/2 is deprecated. Use the new child specifications outlined in the Supervisor module instead
  lib/kaffe/consumer_group/worker/worker_supervisor.ex:14: Kaffe.WorkerSupervisor.start_worker_manager/2

warning: Supervisor.Spec.worker/2 is deprecated. Use the new child specifications outlined in the Supervisor module instead
  lib/kaffe/consumer_group/group_member_supervisor.ex:59: Kaffe.GroupMemberSupervisor.init/1

warning: Supervisor.Spec.worker/3 is deprecated. Use the new child specifications outlined in the Supervisor module instead
  lib/kaffe/consumer_group/worker/worker_supervisor.ex:22: Kaffe.WorkerSupervisor.start_worker/4

warning: Supervisor.Spec.worker/3 is deprecated. Use the new child specifications outlined in the Supervisor module instead
  lib/kaffe/consumer_group/group_member_supervisor.ex:47: Kaffe.GroupMemberSupervisor.start_group_member/5

[britth]

thanks @rodrigues ! 🌟