title: modify font size on y axis for Plotly
body: <p>When I try to modify my y axis title, it just disapears. Modifying the y axis ticks works just fine. Has anyone had this problem? Thanks!</p>
  
  <pre><code>library(plotly)
  set.seed(2017)
  x &lt;- seq(1:10)
  y &lt;- x + rnorm(10)
  plot_ly( x = ~x, y = ~y + rnorm(10)) %&gt;%
       layout(
         xaxis = list(tickfont = list(size = 15)), 
         yaxis = list(tickfont = list(size = 25))) ## This works well.
  
   plot_ly( x = ~x, y = ~y + rnorm(10)) %&gt;%
       layout(
         xaxis = list(tickfont = list(size = 15)), 
         yaxis = list(titlefont = list(size = 25))) ## This makes the y axis label disappear.
  </code></pre>
  
  <p>The goal is to modify the size of the y axis title, not to make it disappear all together. </p>