Error(s) in re-building vignettes:
  ...
--- re-building ‘cubist.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘cubist.Rmd’

--- re-building ‘glm.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘glm.Rmd’

--- re-building ‘lm.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘lm.Rmd’

--- re-building ‘mars.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
Quitting from lines 82-89 (mars.Rmd) 
Error: processing vignette 'mars.Rmd' failed with diagnostics:
formula_ is unknown
--- failed re-building ‘mars.Rmd’

--- re-building ‘non-r.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘non-r.Rmd’

--- re-building ‘ranger.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
Quitting from lines 68-75 (ranger.Rmd) 
Error: processing vignette 'ranger.Rmd' failed with diagnostics:
formula_ is unknown
--- failed re-building ‘ranger.Rmd’

--- re-building ‘regression.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘regression.Rmd’

--- re-building ‘rf.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
Quitting from lines 68-75 (rf.Rmd) 
Error: processing vignette 'rf.Rmd' failed with diagnostics:
formula_ is unknown
--- failed re-building ‘rf.Rmd’

--- re-building ‘save.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘save.Rmd’

--- re-building ‘sql.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘sql.Rmd’

--- re-building ‘tree.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘tree.Rmd’

--- re-building ‘xgboost.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
--- finished re-building ‘xgboost.Rmd’

SUMMARY: processing the following files failed:
  ‘mars.Rmd’ ‘ranger.Rmd’ ‘rf.Rmd’

Error: Vignette re-building failed.
Execution halted