Version of EOSJS
20.0.0-beta2

Describe the bug
When a project that already use babel-polyfill, include this library, an exception occur:

Uncaught Error: only one instance of babel-polyfill is allowed

To Reproduce

check here the code to reproduce:
https://codesandbox.io/s/q33k7vmk14

import '@babel/polyfill';
import { JsSignatureProvider } from 'eosjs';

as far as I know, 3rd party libraries, such this one, should not include babel-polyfill, check the answer here for more info:
https://stackoverflow.com/questions/34962902/should-javascript-library-which-uses-es6-and-es7-features-require-babel-polyfill