title: SetState in an array with React spread operator
body: <p>I have a value in my react state that looks like so:</p>
  
  <pre><code>appointmentsData = {
    "05-01-2018": [
      {
        id: "1",
        friendly: "9:00am - 10:00am",
        openDateTime: "9:00am",
        closeDateTime: "10:00am"
      }
    ]
  };
  </code></pre>
  
  <p>I have a new piece of data:</p>
  
  <pre><code>const newAppt = {"06-30-2018":[]}
  </code></pre>
  
  <p>How do I addon to my data in the state? I tried</p>
  
  <pre><code>this.setState({ ...this.state.appointmentsData, ...newAppt}); 
  </code></pre>
  
  <p>It seems to no be adding onto state though. I get back the same value in the render as before (appointmentData before spread). The newAppt never gets added to the state.</p>
  
  <p>I am trying to get my states desired output to be:</p>
  
  <pre><code>appointmentsData = {
    "05-01-2018": [
      {
        id: "1",
        friendly: "9:00am - 10:00am",
        openDateTime: "9:00am",
        closeDateTime: "10:00am"
      }
    ],
    "06-30-2018": []
  };
  </code></pre>