Update confetti.js

fix randomFrom function to work as intended with smaller numbers.

Right now it will get stuck on the "a" value because the Math.floor rounds down to zero 100% of the time unless (b-a) > 1
Assuming float breaks the rgba color test
Confetti should return a rgba color string FAILED
	Expected 'rgba(90.06, 89.07, 56.94, 0.9923017036760249)' to match /rgba\([0-9]+,\s[0-9]+,\s[0-9]+,\s0(.[0-9]+)?\)/.