Error(s) in re-building vignettes:
  ...
--- re-building ‘europarl.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  The vignette engine knitr::rmarkdown is not available, because the rmarkdown package is not installed. Please install it.
Quitting from lines 22-24 (europarl.Rmd) 
Error: processing vignette 'europarl.Rmd' failed with diagnostics:
there is no package called 'devtools'
--- failed re-building ‘europarl.Rmd’

--- re-building ‘vignette.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  The vignette engine knitr::rmarkdown is not available, because the rmarkdown package is not installed. Please install it.
... adding corpus positions to table 'metadata'
Creating new corpus 'UNGA'
... encoding p-attribute 'word'
... writing tokenstream to disk (directly from R, equivalent to cwb-encode)
... creating indices (in memory)
... writing file: word.corpus
... writing file: word.lexicon
... writing file: word.lexicon.idx
... creating data for new registry file
... writing registry file
Creating new corpus 'AUSTEN'
... encoding p-attribute 'word'
... writing tokenstream to disk (directly from R, equivalent to cwb-encode)
... creating indices (in memory)
... writing file: word.corpus
... writing file: word.lexicon
... writing file: word.lexicon.idx
... creating data for new registry file
... writing registry file
... encoding s-attribute 'book'
Loading required package: NLP
... adding corpus positions to table 'metadata'
Creating new corpus 'REUTERS'
... encoding p-attribute 'word'
... writing tokenstream to disk (directly from R, equivalent to cwb-encode)
... creating indices (in memory)
... writing file: word.corpus
... writing file: word.lexicon
... writing file: word.lexicon.idx
... creating data for new registry file
... writing registry file
... encoding s-attribute 'topics_cat'
... encoding s-attribute 'places'
--- finished re-building ‘vignette.Rmd’

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

Error: Vignette re-building failed.
Execution halted