add middleware thunk

src/configureStore.js

-import { createStore } from 'redux'
+import { createStore, applyMiddleware } from 'redux'
 import reducers from './reducers'
+import thunk from 'redux-thunk'
 
 export default function configureStore() {
-  const store = createStore(reducers)
+  const store = createStore(reducers, applyMiddleware(thunk))
 
   if (module.hot) {
     module.hot.accept(() => {