Error(s) in re-building vignettes:
  ...
--- re-building ‘basics.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) not available. Falling back to R Markdown v1.
Quitting from lines 29-32 (basics.Rmd) 
Error: processing vignette 'basics.Rmd' failed with diagnostics:
there is no package called 'webshot'
--- failed re-building ‘basics.Rmd’

--- re-building ‘doms.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) not available. Falling back to R Markdown v1.
Quitting from lines 34-35 (doms.Rmd) 
Error: processing vignette 'doms.Rmd' failed with diagnostics:
there is no package called 'webshot'
--- failed re-building ‘doms.Rmd’

--- re-building ‘iframes.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) not available. Falling back to R Markdown v1.
Quitting from lines 75-83 (iframes.Rmd) 
Error: processing vignette 'iframes.Rmd' failed with diagnostics:
there is no package called 'webshot'
--- failed re-building ‘iframes.Rmd’

--- re-building ‘pdfs.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) not available. Falling back to R Markdown v1.
Quitting from lines 39-40 (pdfs.Rmd) 
Error: processing vignette 'pdfs.Rmd' failed with diagnostics:
there is no package called 'webshot'
--- failed re-building ‘pdfs.Rmd’

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

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

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

SUMMARY: processing the following files failed:
  ‘basics.Rmd’ ‘doms.Rmd’ ‘iframes.Rmd’ ‘pdfs.Rmd’

Error: Vignette re-building failed.
Execution halted