[custom-set] example and test suite diverge

[NobbZ]

The tests do check for Inspect as foolows:

  test "inspect" do
    assert inspect(CustomSet.new) == "%CustomSet{list: []}"
    assert inspect(CustomSet.new([1,3,2])) == "%CustomSet{list: [1, 2, 3]}"
    assert inspect(CustomSet.new(["A",:b,?C])) == "%CustomSet{list: [67, :b, \"A\"]}"
  end

While the example implementation does implement Inspect as follows:

  def inspect(s, opts) do
    concat ["#<CustomSet ", to_doc(CustomSet.to_list(s), opts), ">"]
  end

Before commit 9222be9 the example and the test matched.