Support React 17

[lephleg]

Hello!

Create-react-app defaults to 17.0.1 now causing various issues with new projects.

% npm install notistack
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! While resolving: client@0.1.0
npm ERR! Found: react@17.0.1
npm ERR! node_modules/react
npm ERR!   react@"^17.0.1" from the root project
npm ERR!   peer react@"^16.8.0 || ^17.0.0" from @material-ui/core@4.11.2
npm ERR!   node_modules/@material-ui/core
npm ERR!     @material-ui/core@"^4.11.2" from the root project
npm ERR!     peer @material-ui/core@"^4.0.0" from notistack@1.0.2
npm ERR!     node_modules/notistack
npm ERR!       notistack@"*" from the root project
npm ERR!   1 more (react-dom)
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer react@"^16.8.0" from notistack@1.0.2
npm ERR! node_modules/notistack
npm ERR!   notistack@"*" from the root project
npm ERR!
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.

Any plans to support React 17 before MUI v5?

[iamhosseindhv]

Fixed in #339

You can now use React 17 compatible version v1.0.3 (latest stable) or v1.0.4-alpha.0 (alpha next)