title: render plot doesn't appear
body: <p>I am using the code below to render a plot but the plot doesn't appear.</p>
  
  <pre><code>---
  title: "Untitled"
  author: "George"
  date: "12/3/2018"
  output:
      flexdashboard::flex_dashboard:
      orientation: rows
  runtime: shiny
  ---
  
      ```{r global, include=FALSE}
  knitr::opts_chunk$set(echo = FALSE)
  library(flexdashboard)
  library(dplyr)
  library(GGally)
  
  
  x &lt;- c(1,2,3)
  y &lt;- c(11,22,33)
  z &lt;- data.frame(x, y)
  ```
  
  Introduction
  =======================================================================
  
  ### General info
  
  - A
  
  - B
  
  
  
  Corr
  =======================================================================
  
  ### Correlation
  ```{r include=TRUE, results='hide'}
  renderPlot({
      GGally::ggpairs(z)
  })
  
  ```
  </code></pre>