Error(s) in re-building vignettes:
  ...
--- re-building ‘bi-objective.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.
Loading required namespace: rmarkdown
PhantomJS not found. You can install it with webshot::install_phantomjs(). If it is installed, please make sure the phantomjs executable can be found via the PATH variable.
Warning in normalizePath(f2) :
  path[1]="webshot6169298a6304.png": No such file or directory
Warning in file(con, "rb") :
  cannot open file 'webshot6169298a6304.png': No such file or directory
Quitting from lines 285-286 (bi-objective.Rmd) 
Error: processing vignette 'bi-objective.Rmd' failed with diagnostics:
cannot open the connection
--- failed re-building ‘bi-objective.Rmd’

--- re-building ‘polytope_2d.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 ‘polytope_2d.Rmd’

--- re-building ‘polytope_3d.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.
Loading required namespace: rmarkdown
PhantomJS not found. You can install it with webshot::install_phantomjs(). If it is installed, please make sure the phantomjs executable can be found via the PATH variable.
Warning in normalizePath(f2) :
  path[1]="webshot5ea45457245.png": No such file or directory
Warning in file(con, "rb") :
  cannot open file 'webshot5ea45457245.png': No such file or directory
Quitting from lines 62-64 (polytope_3d.Rmd) 
Error: processing vignette 'polytope_3d.Rmd' failed with diagnostics:
cannot open the connection
--- failed re-building ‘polytope_3d.Rmd’

SUMMARY: processing the following files failed:
  ‘bi-objective.Rmd’ ‘polytope_3d.Rmd’

Error: Vignette re-building failed.
Execution halted