Adiciona referências.

slides/config/refs.bib

+@book{gillespie2016efficient,
+  title={Efficient R Programming: A Practical Guide to Smarter Programming},
+  author={Gillespie, C. and Lovelace, R.},
+  isbn={9781491950753},
+  url={https://bookdown.org/csgillespie/efficientR/},
+  year={2016},
+  publisher={O'Reilly Media}
+}