add2 and add4 chords not correctly generated

[romeoleung]

When creating chords with added tone, if the tone number is 2 or 4, it only generates a triad without the added notes.
Example:
var c4 = teoria.note("C4");
teoria.Chord(c4, "add2").simple(); // => Only getting ["c", "e", "g"] . expected is to get ["c", "d", "e", "g"]
teoria.Chord(c4, "add4").simple(); // => Only getting ["c", "e", "g"] . expected is to get ["c", "e", "f", "g"]

Adding this code after line 1188 temporarily resolves the issue, but the note's is always added to the last:

else if (next === '2')
    additionals.push('M2');
else if (next === '4')
   additionals.push('P4');

Hopefully this could be fixed. Thank you!