Fix indication to inexistant `is_record` macro

The macro `is_record/3` doesn't exist.

```iex
iex(1)> is_record 1
false
iex(2)> is_record 1, 1
false
iex(3)> is_record 1, 1, 1
** (UndefinedFunctionError) undefined function: IEx.Helpers.is_record/3
    IEx.Helpers.is_record(1, 1, 1)
    erl_eval.erl:569: :erl_eval.do_apply/6
    src/elixir.erl:138: :elixir.eval_forms/3
```