Fix example code in distributed-tasks-and-configuration

[1st8]

Usage of Task.Supervisor.async/4 is meant instead.

Result of running existing example

iex(bar@Christophs-MBP)1> Task.Supervisor.async {KV.RouterTasks, :"foo@Christophs-MBP"}, [Kernel, :node, []]
** (EXIT from #PID<0.101.0>) an exception was raised:
    ** (BadFunctionError) expected a function, got: [Kernel, :node, []]
        :erlang.apply/2
        (elixir) lib/task/supervised.ex:89: Task.Supervised.do_apply/2
        (elixir) lib/task/supervised.ex:40: Task.Supervised.reply/5
        (stdlib) proc_lib.erl:240: :proc_lib.init_p_do_apply/3

Interactive Elixir (1.2.0) - press Ctrl+C to exit (type h() ENTER for help)

Result of running changed example

iex(bar@Christophs-MBP)2> Task.Supervisor.async {KV.RouterTasks, :"foo@Christophs-MBP"}, Kernel, :node, []
%Task{owner: #PID<0.144.0>, pid: #PID<12960.109.0>, ref: #Reference<0.0.8.533>}