equal fn有误

[givebest]

function equal (a, b) { return Math.abs(a, b) < Number.EPSILON }
return 处应为：
return Math.abs(a - b) < Number.EPSILON

@see https://github.com/getify/You-Dont-Know-JS/blob/master/types%20%26%20grammar/ch2.md#small-decimal-values

[shanyue]

手误，非常感谢！