.bib updates

packages.bib

@@ -3,27 +3,27 @@ @Manual{R-base
   author = {{R Core Team}},
   organization = {R Foundation for Statistical Computing},
   address = {Vienna, Austria},
-  year = {2018},
+  year = {2019},
   url = {https://www.R-project.org/},
 }
 @Manual{R-bookdown,
   title = {bookdown: Authoring Books and Technical Documents with R Markdown},
   author = {Yihui Xie},
-  year = {2018},
-  note = {R package version 0.9},
+  year = {2019},
+  note = {R package version 0.12},
   url = {https://CRAN.R-project.org/package=bookdown},
 }
 @Manual{R-knitr,
   title = {knitr: A General-Purpose Package for Dynamic Report Generation in R},
   author = {Yihui Xie},
-  year = {2018},
-  note = {R package version 1.21},
+  year = {2019},
+  note = {R package version 1.24},
   url = {https://CRAN.R-project.org/package=knitr},
 }
 @Manual{R-rmarkdown,
   title = {rmarkdown: Dynamic Documents for R},
   author = {JJ Allaire and Yihui Xie and Jonathan McPherson and Javier Luraschi and Kevin Ushey and Aron Atkins and Hadley Wickham and Joe Cheng and Winston Chang and Richard Iannone},
-  year = {2018},
-  note = {R package version 1.11},
+  year = {2019},
+  note = {R package version 1.15},
   url = {https://CRAN.R-project.org/package=rmarkdown},
 }