Add UMD build

[Strajk]

Hi :wave: first of all, thx for amazing for on this lib 🤟

I would like to use it in Chrome extension I'm working on, but:

• I don't have a compile step -> cannot use the module version
• Chrome Web Store disallow minified code in extensions -> cannot use minified IIFE version

This PR adds .umd.js bundle which have UMD preamble

(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
    typeof define === 'function' && define.amd ? define(factory) :
    (global = global || self, global.Notyf = factory());
}(this, (function () { 'use strict';

// ...

Closes #78

[Strajk]

To consider:

• Add more info about it to README?
• Add more info about it to recipes/global.md?

[caroso1222]

This is amazing, thank you!