title: Uncaught TypeError: Object(...) is not a function when invoke createStore
body: <p>I was runnig a react-app and using react-redux to manage my state. It works well at first, But it crashed suddenly.I can't createStore any longer.It just told me "Uncaught TypeError: Object(...) is not a function"</p>
  
  <p>I tried to re-install a low version react-redux as others told, but it doesn't work.
  I cleared the cookies, restart the project, and nothing changed.
  I just try the code as the example provided by redux offical size, and it sucks in the first step, which invoke createStore(reducer).</p>
  
  <p>the dependencies version:   </p>
  
  <pre><code>"react": "^16.9.0",  
  "react-dom": "^16.9.0",  
  "react-redux": "^7.1.1",  
  "react-scripts": "3.1.1",  
  "redux": "^4.0.4"  
  </code></pre>
  
  <p>the index.js</p>
  
  <pre><code>import React,{ createStore }  from 'react'
  import { render } from 'react-dom'
  import { Provider } from 'react-redux'
  
  import App from './App'
  import * as serviceWorker from './serviceWorker'
  import reducer from './reducer'
  
  const store = createStore(reducer)
  
  // ReactDOM.render(&lt;App /&gt;, document.getElementById('root'));
  render (
    &lt;Provider store={store}&gt;
      &lt;App /&gt;
    &lt;/Provider&gt;
   ,
  
    // document.querySelector('#root')
    document.getElementById('root')
  )
  
  serviceWorker.unregister();
  </code></pre>
  
  <p>and reducer.js</p>
  
  <pre><code>export default  (state , action) =&gt; {
      switch(action.type) {
          case 'INCREASE_COUNTER': 
              return {
                  ...state,
                  counter: state.counter + 1
              }
          default:
              return state
      }
  }
  </code></pre>
  
  <p>I just wanted the app render successfully, it works fine before the problem occured. But I did nothing it just crash,and createStore didn't work any longer. It's really weird.</p>