Error(s) in re-building vignettes:
  ...
--- re-building ‘modelplotr.Rmd’ using rmarkdown

Quitting from lines 484-485 [plot_roi] (modelplotr.Rmd)
Error: processing vignette ‘modelplotr.Rmd’ failed with diagnostics:
invalid non-character version specification ‘x’ (type: double)
--- failed re-building ‘modelplotr.Rmd’

SUMMARY: processing the following file failed:
  ‘modelplotr.Rmd’

Error: Vignette re-building failed.
Execution halted
Error(s) in re-building vignettes:
  ...
--- re-building ‘modelplotr.Rmd’ using rmarkdown

Quitting from lines 484-485 [plot_roi] (modelplotr.Rmd)
Error: processing vignette 'modelplotr.Rmd' failed with diagnostics:
invalid non-character version specification 'x' (type: double)
--- failed re-building ‘modelplotr.Rmd’

SUMMARY: processing the following file failed:
  ‘modelplotr.Rmd’

Error: Vignette re-building failed.
Execution halted