title: Why can't I chain state.get('something').filter with immutable.js?
body: <h2>What am I doing wrong?</h2>
  
  <p>I want to filter the <em>steps</em> key inside my <em>state</em> using <code>get('..')</code> and <code>filter</code> but I can't manage to do it.</p>
  
  <p><strong>I have this function:</strong></p>
  
  <pre><code>function visibleSteps(state) {
    return state.get('steps').filter((step) =&gt; {
      return step.display
    })
  }
  </code></pre>
  
  <p><strong>When tested with this example:</strong></p>
  
  <pre><code>describe('visibleSteps', () =&gt; {
    it('should show the steps with display true and their title', () =&gt; {
       const state = Map({
          steps: {
              0: {
                  display: false
              },
              1: {
                  display: true,
                  title: "A title"
              },
              2: {
                  display: true,
              },
              3: {
                 display: false,
              }
          }
      })
  
      expect(visibleSteps(state).size).to.equal(2)
    })
  })
  </code></pre>
  
  <p><strong>I get this error:</strong></p>
  
  <pre><code>TypeError: state.get(...).filter is not a function
  </code></pre>
  
  <p>How would the man do this? </p>