Fix for IE11 - don't use destructuring assign

[jeffsenn]

Doesn't work in IE11 due to this line in index.js:

const {float32, fract32} = require('to-float32')

Fix (remove destructing assignment):

const to_float32 = require('to-float32')

const float32 = to_float32.float32

const fract32 = to_float32.fract32