title: Immutable.js setIn not working
body: <p>I have the following list that I'm trying to return a new List from, but I keep getting the error shown below. Any thoughts?</p>
  
  <pre><code>export const questions = List([
    {uuid: uuid(), order: 0, text: 'Which country do you live in?', choices: [
      { choice: 'United States', added: true },
      { choice: 'Canada', added: true },
      { choice: 'Australia', added: true }
    ]},
    {uuid: uuid(), order: 1, text: 'Which country were you born in?', choices: [
      { choice: 'Mexico', added: true },
      { choice: 'California', added: true },
      { choice: 'Seoul', added: true }
    ]}
  ]);
  
  
  questions.setIn([0, 'text'], 'changed') 
  </code></pre>
  
  <p>Results in this error:</p>
  
  <pre><code>immutable.js:870 Uncaught Error: invalid keyPath
      at invariant (immutable.js:870)
      at updateInDeepMap (immutable.js:1974)
      at updateInDeepMap (immutable.js:1980)
      at List.Map.updateIn (immutable.js:1278)
      at List.Map.setIn (immutable.js:1256)
      at eval (eval at ./src/reducers/questionsList.js (questionsList.js:17), &lt;anonymous&gt;:1:11)
  </code></pre>