title: Changing tick labels with plotnine
body: <p>I'm using <a href="https://github.com/has2k1/plotnine" rel="nofollow noreferrer">plotnine</a> to generate a scatterplot where the x-axis is pandas.Timestamp objects. </p>
  
  <p>Currently, the x tick labels (e.g., "2017-07-01") are running into each other. I'd like to be able to do an arbitrary transformation of the tick labels. How do I change the x tick labels on the plot? </p>
  
  <p>It looks like I could do something like <code>+ scale_x_continuous(labels=???)</code> but I don't know what argument to pass to labels.</p>