   [Erlang's :os.cmd/1 function](http://www.erlang.org/doc/man/os.html#cmd-1).
   """
   @spec cmd(binary, [binary], Keyword.t) ::
-        {:ok, Collectable.t, exit_status :: non_neg_integer} | {:error, atom}
+        {Collectable.t, exit_status :: non_neg_integer}
   def cmd(command, args, opts \\ []) when is_binary(command) and is_list(args) do
     command = String.to_char_list(command)
 


    * `:eagain` - there are no more available operating system processes

    * `:enametoolong` - the external command given was too long.

    * `:emfile` - there are no more available file descriptors
      (for the operating system process that the Erlang emulator runs in)

  `command` is expected to be an executable available in PATH
  unless an absolute path is given.

  `args` must be a list of strings which are not expanded
  in any way. For example, this means wildcard expansion will
  not happen unless `Path.wildcard/2` is used. On Windows though,
  wildcard expansion is up to the program.
