title: Reactjs push new element to nested state
body: <p>I'm new to javascript and react, I try to push a new element to an array inside the state but there's no success.</p>
  
  <pre><code>state = {
   columns: [
    {
     id: 122,
     items: [{text:'abc'},{text:'cde'}]
    },
    {
     id: 143,
     items: []
    }
   ]
   }
  
     addItem(columnId,text) {
       const newItem = {text: text}
     //this.setState(...)
     }
  </code></pre>
  
  <p>Basically, I have an addItem function with given columnId and some text content, I want to push a new item to the items array inside the column with given columnId.</p>
  
  <p>I heard that it'd be much easier with the help of immutability-helper, is that right?</p>