title: xaringan slide separator not separating slides
body: <p>In this example <code>xaringan</code> presentation, why are both the <code>## blank page</code> and the <code>leaflet</code> map on the same slide, given I've separated them by the new-slide separator <code>---</code> ?</p>
  
  <pre><code>---
  title: "map test"
  output:
    xaringan::moon_reader:
      css: ["default"]
      nature:
        highlightLines: true
  ---
  
  ```{r setup, include=FALSE}
  knitr::opts_chunk$set(echo = TRUE)
  ```
  
  
  ## blank page
  
  content 
  
  --- 
  
  leaflet page
  
  ```{r}
  library(leaflet)
  leaflet() %&gt;%
    addTiles()
  
  ```
  
  ---
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/AunFv.png" rel="noreferrer"><img src="https://i.stack.imgur.com/AunFv.png" alt="enter image description here"></a></p>