Add React 17 to Peer dependencies

[RobinPayne]

Package.json only lists ^16.8.0 as being compatible. with this library. I updated the peer dependencies so I don't get any problems with npm install.

When I try and install this library in my project I get an error similar to:

npm WARN Could not resolve dependency:
npm WARN peer react@"^16.8.0" from [email protected]
npm WARN node_modules/react-window-scroller
npm WARN   react-window-scroller@"1.0.10" from the root project
npm WARN 
npm WARN Conflicting peer dependency: [email protected]
npm WARN node_modules/react
npm WARN   peer react@"^16.8.0" from [email protected]
npm WARN   node_modules/react-window-scroller
npm WARN     react-window-scroller@"1.0.10" from the root project

This change fixes this.