react-redux v6.0.0 uses the new context api provided by React and in order for it work, either you need to downgrade react-redux to v5.x.x or upgrade react and react-dom to v16.4 or above
If you are using yarn, you can run
yarn upgrade react react-dom
else with npm you can run
npm update react react-dom
You could also change the versions manually in package.json and run yarn install or npm install