title: Adjust hexbin legend breaks
body: <p>In this example of a hexbin plot, the legend on the right has 10 levels/classes/breaks. Does anyone know how to change the number of levels? Say I want to change it to 5 or something.</p>
  
  <pre><code>  library(hexbin)
    x=rnorm(1000, mean = 50, sd = 1)
    y=rnorm(1000, mean = 30, sd = 0.5)
    df &lt;- data.frame(x,y)
    #plot(df)
  
    hb &lt;- hexbin(x=df$x, df$y)
    #hb &lt;- hexbin(x=df$x, df$y,xbins=30)
    #plot(hb)
    gplot.hexbin(hb)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/tiEn3.jpg" alt="hexbin"></p>