bugfix: incorrect apply_patch for the move operation for the same list

[Valian]

When using the project, I noticed move operation is not correctly applied when both source and target are coming from the same list. Eg this test was failing.

  # Move within the same list
  test "move element within the same list" do
    move = %Jsonpatch.Operation.Move{from: "/arr/0", path: "/arr/2"}
    target = %{"arr" => ["a", "b", "c"]}

    assert Jsonpatch.Operation.Move.apply(move, target, []) ==
             {:ok, %{"arr" => ["b", "c", "a"]}}
  end

Reason

We were first inserting and then removing. If it happened within the same list, remove operation might have targeted invalid object because indices are updated after insertion. It should first remove and then insert.

Solution

Now order of operations is correct: First, we determine which element should be inserted. Next, we remove that element, and as a last step we add previously remembered element into desired place.

[corka149]

Please update expected error values in the tests. Else LGTM!