title: Adding second Y axis on ggplotly
body: <p>I have created the following dataframe object and graph using plotly and ggplot</p>
  
  <pre><code>library(ggplot2)
  library(plotly)
  
  rdate &lt;- function(x,
                min = paste0(format(Sys.Date(), '%Y'), '-01-01'),
                max = paste0(format(Sys.Date(), '%Y'), '-12-31'),
                sort = TRUE) {          
    dates &lt;- sample(seq(as.Date(min), as.Date(max), by = "day"), x, replace=TRUE)
    if (sort == TRUE) {
      sort(dates)
    } else {
      dates
    }
  }
  
  DF&lt;-data.frame(Date = rdate(100))
  DF$variable&lt;-LETTERS[seq( from = 1, to = 10 )]
  DF$Value&lt;-round(runif(1:nrow(DF),min = 10, max = 50))
  </code></pre>
  
  <p>Next I have created a plot object with ggplot</p>
  
  <pre><code> p &lt;- ggplot(DF, aes(x = Date, y = Value, colour = variable)) + 
    geom_line() + 
    ylab(label="Sellcount") + 
    xlab("Sell Week")
    p&lt;-p + scale_y_continuous(sec.axis = dup_axis())
    ggplotly(p)
  </code></pre>
  
  <p>IF i plot p using plot(p), the graph has 2 yaxes as I expect. However, when I use ggplotly(p) to plot the graph, only one Y axis is generated. I am unable to find any literature on the internet regarding the same. I request someone to help me in this.</p>