Error(s) in re-building vignettes:
--- re-building 'Basic_Tabular.Rmd' using rmarkdown
--- finished re-building 'Basic_Tabular.Rmd'

--- re-building 'audio.Rmd' using rmarkdown
--- finished re-building 'audio.Rmd'

--- re-building 'audio2tf.Rmd' using rmarkdown
--- finished re-building 'audio2tf.Rmd'

--- re-building 'basic_img_class.Rmd' using rmarkdown
--- finished re-building 'basic_img_class.Rmd'

--- re-building 'bayes_opt.Rmd' using rmarkdown
--- finished re-building 'bayes_opt.Rmd'

--- re-building 'callbacks.Rmd' using rmarkdown
--- finished re-building 'callbacks.Rmd'

--- re-building 'catalyst.Rmd' using rmarkdown
--- finished re-building 'catalyst.Rmd'

--- re-building 'custom_img.Rmd' using rmarkdown
--- finished re-building 'custom_img.Rmd'

--- re-building 'data_aug.Rmd' using rmarkdown
--- finished re-building 'data_aug.Rmd'

--- re-building 'gpt.Rmd' using rmarkdown
--- finished re-building 'gpt.Rmd'

--- re-building 'head_pose.Rmd' using rmarkdown
--- finished re-building 'head_pose.Rmd'

--- re-building 'lightning.Rmd' using rmarkdown
--- finished re-building 'lightning.Rmd'

--- re-building 'low.Rmd' using rmarkdown
--- finished re-building 'low.Rmd'

--- re-building 'medical_dcm.Rmd' using rmarkdown
--- finished re-building 'medical_dcm.Rmd'

--- re-building 'migrating_ignite.Rmd' using rmarkdown
--- finished re-building 'migrating_ignite.Rmd'

--- re-building 'migrating_pytorch.Rmd' using rmarkdown
--- finished re-building 'migrating_pytorch.Rmd'

--- re-building 'multilabel.Rmd' using rmarkdown
--- finished re-building 'multilabel.Rmd'

--- re-building 'obj_detect.Rmd' using rmarkdown
--- finished re-building 'obj_detect.Rmd'

--- re-building 'optimizer.Rmd' using rmarkdown
--- finished re-building 'optimizer.Rmd'

--- re-building 'question_answering.Rmd' using rmarkdown
--- finished re-building 'question_answering.Rmd'

+-+question_answering.html
--- re-building 'super_res_gan.Rmd' using rmarkdown
--- finished re-building 'super_res_gan.Rmd'

--- re-building 'textclassification.Rmd' using rmarkdown
--- finished re-building 'textclassification.Rmd'

--- re-building 'textsummarize.Rmd' using rmarkdown
--- finished re-building 'textsummarize.Rmd'

--- re-building 'time_series.Rmd' using rmarkdown
--- finished re-building 'time_series.Rmd'

SUMMARY: processing the following file failed:
  'question_answering.Rmd'

Error: Vignette re-building failed.
Execution halted