Dealing with lack of internet while knitting the vignettes

My hunch is that this was a temporary issue where the internet connection might have been down during the check. But we should anticipate and deal with this anyway. That is, we should evaluate this vignette, or at least the relevant chunks, only when internet is available (using curl::has_internet()).

cf. https://www.r-project.org/nosvn/R.check/r-oldrel-windows-x86_64/datawizard-00check.html

Version: 0.9.1
Check: re-building of vignette outputs
Result: ERROR 
  Error(s) in re-building vignettes:
  --- re-building 'selection_syntax.Rmd' using rmarkdown
  --- finished re-building 'selection_syntax.Rmd'
  
  --- re-building 'standardize_data.Rmd' using rmarkdown
  
  Quitting from lines 204-218 [unnamed-chunk-9] (standardize_data.Rmd)
  Error: processing vignette 'standardize_data.Rmd' failed with diagnostics:
  cannot open the connection to 'https://raw.githubusercontent.com/neuropsychology/psycho.R/master/data/emotion.rda'
  --- failed re-building 'standardize_data.Rmd'

Start with the network-dependent chunk in vignettes/standardize_data.Rmd, especially lines 204-218, and review the reported vignette rebuild failure. Use curl::has_internet() as the issue suggests to conditionally handle that content, then rebuild the vignettes and confirm the check succeeds when internet access is unavailable.