title: Set levels in scale_fill_distiller
body: <p>I am trying to control the levels set by ggplot2 scale_fill_distiller, ideally I would like to show the lower levels of "values" better. The plot below shows no variation - I suppose - because the numbers are close to 0. </p>
  
  <p>The data is hosted here:
  <a href="http://pasted.co/4aa6411c" rel="nofollow noreferrer">http://pasted.co/4aa6411c</a></p>
  
  <p>And I am plotting with:</p>
  
  <pre><code>require(ggplot2)
  ggplot(data, aes(Years, Age, fill = values)) + geom_tile() + 
  scale_fill_distiller(palette = "Spectral") 
  </code></pre>
  
  <p>Which gives the result:</p>
  
  <p><a href="https://i.stack.imgur.com/UfTTB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/UfTTB.png" alt="enter image description here"></a></p>