Fix warnings for deprecated APIs

[skirunman]

Fix warnings for deprecated use of Material-UI fab and raised button variants and with new Fab component and contained button variant. Fixes #46
See https://material-ui.com/api/button/

[leMaik]

Thank you. 👍 As said in #46 I'll wait for v4 to be released before merging this PR.

[skirunman]

Only problem with waiting is anyone in production, like us, is going to have those warnings show up in their user's browser console. We are definitely going to get some support calls on that. Also, my guess is that most, if not all, users of this component are tracking the latest releases of Material-UI as there are many bug fixes and enhancements.

Would it not be possible to simply do a 3.0.0 release with these changes now with peer dependencies on "@material-ui/core": "^3.6.0" and "@material-ui/icons": "^3.0.1" and then do a 4.0.0 release when Material-UI 4 comes out some time next year? I really appreciate your consideration as this is an issue for us. Thanks!

[leMaik]

@skirunman Good idea, I'll release it soon.

Offtopic: The warnings show up in your user's browser consoles? 😱 You should fix your bundler settings in order to ship production versions of prop-types that don't print warnings in production environments. They are just warnings, after all.

[skirunman]

@leMaik Thanks!