title: Plotly R: can't make custom xaxis date ranges to work
body: <p>This should be very simple (I think) and yet I can't get this to work for some reason. I have data like this:</p>
  
  <pre><code>df
             x y
  1 2016-08-12 1
  2 2016-08-13 2
  3 2016-08-14 3
  4 2016-08-15 4
  5 2016-08-16 5
  
  str(df)
  'data.frame':   5 obs. of  2 variables:
   $ x: Date, format: "2016-08-12" "2016-08-13" ...
   $ y: int  1 2 3 4 5
  </code></pre>
  
  <p>I am using plotly as follows, but it does not adjust the xaxis range to my specified custom values. Instead, uses the range of the data:</p>
  
  <pre><code>library(plotly)
  plot_ly(df, x = x, y = y) %&gt;% layout(xaxis = list(range = c(as.Date('2016-08-01'), as.Date('2016-08-31'))))
  </code></pre>
  
  <p>On the other hand, if I have numeric data like this:</p>
  
  <pre><code>df
    x y
  1 1 1
  2 2 2
  3 3 3
  4 4 4
  5 5 5
  </code></pre>
  
  <p>And specify a custom range like this, it works fine:</p>
  
  <pre><code>plot_ly(df, x = x, y = y) %&gt;% layout(xaxis = list(range = c(-5, 10)))
  </code></pre>
  
  <p>What am I missing in making data ranges work?</p>