Unnecessary `p1 > 0` check in `parse`

The else if != 0 check [here](https://github.com/rawify/Fraction.js/blob/95a94550641ecfedd85241405e02f966938f4b89/src/fraction.js#L177) is superfluous because 0 is already covered by the % 1 === 0 condition two lines above.