Error(s) in re-building vignettes:
--- re-building ‘plotting_functions.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  The vignette engine knitr::rmarkdown is not available, because the rmarkdown package is not installed. Please install it.
trying URL 'https://www.imbi.uni-freiburg.de/imbi/Royston-Sauerbrei-book/Multivariable_Model-building/downloads/datasets/adv_prostate_ca.zip'
Content type 'text/html; charset=utf-8' length 34677 bytes (33 KB)
==================================================
downloaded 33 KB

Quitting from lines 28-65 (plotting_functions.Rmd) 
Error: processing vignette 'plotting_functions.Rmd' failed with diagnostics:
cannot open the connection
--- failed re-building ‘plotting_functions.Rmd’

--- re-building ‘subbuild_function.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  The vignette engine knitr::rmarkdown is not available, because the rmarkdown package is not installed. Please install it.
trying URL 'https://www.imbi.uni-freiburg.de/imbi/Royston-Sauerbrei-book/Multivariable_Model-building/downloads/datasets/adv_prostate_ca.zip'
Content type 'text/html; charset=utf-8' length 34677 bytes (33 KB)
==================================================
downloaded 33 KB

Quitting from lines 27-38 (subbuild_function.Rmd) 
Error: processing vignette 'subbuild_function.Rmd' failed with diagnostics:
cannot open the connection
--- failed re-building ‘subbuild_function.Rmd’

--- re-building ‘subtee_package.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  The vignette engine knitr::rmarkdown is not available, because the rmarkdown package is not installed. Please install it.
trying URL 'https://www.imbi.uni-freiburg.de/imbi/Royston-Sauerbrei-book/Multivariable_Model-building/downloads/datasets/adv_prostate_ca.zip'
Content type 'text/html; charset=utf-8' length 34677 bytes (33 KB)
==================================================
downloaded 33 KB

Quitting from lines 32-45 (subtee_package.Rmd) 
Error: processing vignette 'subtee_package.Rmd' failed with diagnostics:
cannot open the connection
--- failed re-building ‘subtee_package.Rmd’

SUMMARY: processing the following files failed:
  ‘plotting_functions.Rmd’ ‘subbuild_function.Rmd’ ‘subtee_package.Rmd’

Error: Vignette re-building failed.
Execution halted