Upgrade to Webpack 4 and Babel 7

[jaytula]

@cookpete

This is exactly a regular issue. Just wanted to reach out to you. First off, excellent project you have here. It's hard to imagine how much work this took. Kudos to you!

I forked your repo in an attempt to fix the console.warn's of React lifecycle methods being deprecated in React 17 by re-implementing in componentDidUpdate. This led me down a bit of a rabbit hole in that npm packages used are a bit dated (e.g. Webpack 3, Babel < 7) and it seemed like a better choice to make the leap and break stuff by upgrading all to the latest packages. Anyhow, I did exactly that and ran into problem after problem but pushed through it and eventually got it to run and build.

I thought it wouldn't be wise to create a pull request without first asking because the changes are massive. Totally understand if you don't have time for it but would be grateful if you could review the changes and provide any feedback. Thanks for your time!

https://github.com/jaytula/react-player/commits/master