const used, and then MyComponent is rebound

In the example code, 

```
const MyComponent = React.createClass({
  statics: {
    getStores(props) {
      return [myStore]
    },
    getPropsFromStores(props) {
      return myStore.getState()
    }
  },
  render() {
    // Use this.props like normal ...
  }
})
MyComponent = connectToStores(MyComponent)
```

MyComponent should be defined with `let`
