title: Cannot disable R markdown output from gridExtra (additional comment)
body: <p>In my r markdown report i use 2 chunks. </p>
  
  <p>First:</p>
  
  <pre><code>```{r, include = FALSE, echo=FALSE, results='asis'}```
  </code></pre>
  
  <p>Where i load all packages and do computation.</p>
  
  <p>And second</p>
  
  <pre><code>{r, fig.margin = TRUE, fig.width=10,
  fig.height=4.5, echo=FALSE, results='asis', 
  message=FALSE, warning = FALSE} 
  </code></pre>
  
  <p>Where i have for loop where I filter data I producent in first chunk, and make ggplots for each i. </p>
  
  <p>My problem is that, when i produce 2 plots in second chunk i combine them in one grid by grid.arrange, but there is additional comment I don't want to show.</p>
  
  <pre><code>TableGrob (2 x 2) "arrange": 2 grobs
    z     cells    name           grob
  1 1 (1-2,1-1) arrange gtable[layout]
  2 2 (1-2,2-2) arrange gtable[layout]
  </code></pre>
  
  <hr>
  
  <pre><code>title: "Test"
  author: "Maybe It's You"
  date: "2016.09.01"
  output: pdf_document
  ---
  
  ```{r setup, include=FALSE}
  knitr::opts_chunk$set(echo = TRUE)
  library(grid)
  library(gridExtra)
  library(ggplot2)
  
  lay &lt;- rbind(c(1,2),
               c(1,2))
  gs &lt;- list()
  
  ```
  
  
  ```{r cars}
  summary(cars)
  ```
  
  ## Including Plots
  
  You can also embed plots, for example:
  
  ```{r pressure, echo=FALSE, results='asis', message=FALSE, warning = FALSE}
  p1 &lt;- qplot(1:10)
  p2 &lt;- qplot(1:10)
  gs[[1]] &lt;- p1
  gs[[2]] &lt;- p2          
  
  
  wykres &lt;- grid.arrange(grobs = gs, layout_matrix = lay)
  print(wykres)
  
  ```
  </code></pre>
  
  <h2>Fragment of result with gridExtra comment (TablGrob...)</h2>
  
  <p><a href="https://i.stack.imgur.com/fr1cJ.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/fr1cJ.jpg" alt="Pic of pdf.output"></a></p>