fix: parse ellipsis_op as unary operator

[doorgan]

... + 1 * 2 is not parsed the same as with the elixir parser

Spitfire:

{:+, [line: 1, column: 5], [{:..., [line: 1, column: 1], []}, {:*, [line: 1, column: 9], [1, 2]}]}

Elixir:

{:+, [line: 1, column: 5], [{:..., [line: 1, column: 1], []}, {:*, [line: 1, column: 9], [1, 2]}]}

The problem was that ... was parsed as an empty node, like the ones occurring at typespecs (eg @type foo :: [atom(), ...]) but never as a unary operator.
The fix is to consider it a unary_op if it's not followed by a terminal, then parse the right hand side.