Allocate is raising an ArgumentError when passing rationals

[alexdunae]

Hi there -- thanks for the great gem. I've run into an issue passing an array of rational numbers to allocate. You can reproduce it like so:

> ratios = 7.times.map { Rational(950, 6650) } # 7 x 1/7
> Money.us_dollar(6650).allocate(ratios)
ArgumentError: splits add to more then 100%

Setting different conversion_precision values does change things (e.g. it works at 17 and 14 but not 15) but not predictably.

[antstorm]

Thank you for finding and fixing it!