use configureStore in README

[phryneas]

Since redux 4.2.0, createStore is deprecated in favor of configureStore. This updates the README to use the recommended function.

[phryneas]

Could you please get this merged? It's just a (really necessary) docs update.

[yestay90]

@phryneas , thanks for your PR. I had problem with persistStore which threw error max calls stack exceeded . The problem was I set persistStore inside of function and exported function. Later, I used that function inside of useEffect when app loads. After looking at your PR I realized that instead exporting function, I need to export variable. And this solved my error! I feel happy now)) Thanks a lot.