title: pandoc-citeproc error 83 with Rmarkdown file
body: <p>I have the following document, that I am trying to compile with Rstudio:</p>
  
  <pre><code>---
  title:
  shorttitle:
  author: 
  
  bibliography:
    - library.bib
  
  output: papaja::apa6_pdf
  ---
  
  ```{r message = FALSE, warning = FALSE}
  library("papaja")
  apa_prepare_doc() # Prepare document for rendering
  ```
  # Introduction
  
  @Bakan1966
  
  # References
  ```{r create_r-references}
  r_refs(file = "r-references.bib")
  ```
  </code></pre>
  
  <p>When I run knit, it compiles the .md file, but pandoc gives an error:</p>
  
  <pre><code>pandoc-citeproc: "stdin" (line 232, column 2):
  unexpected "a"
  expecting "c", "C", "p", "P", "s" or "S"
  pandoc: Error running filter /Applications/RStudio.app/Contents/MacOS/pandoc/pandoc-citeproc
  Error: pandoc document conversion failed with error 83
  In addition: Warning messages:
  1: In yaml::yaml.load(enc2utf8(string), ...) :
    NAs introduced by coercion: 1,2,3 is not an integer
  2: In yaml::yaml.load(enc2utf8(string), ...) :
    NAs introduced by coercion: 1,2,3 is not an integer
  Execution halted
  </code></pre>
  
  <p>I have found similar problems on different topics around but none of the proposed solutions worked for me...</p>