Error(s) in re-building vignettes:
  ...
--- re-building ‘rxnat.Rmd’ using rmarkdown
Quitting from lines 133-135 (rxnat.Rmd) 
Error: processing vignette 'rxnat.Rmd' failed with diagnostics:
gnutls_handshake() failed: Error in the pull function.
--- failed re-building ‘rxnat.Rmd’

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

Error: Vignette re-building failed.
Execution halted
Error(s) in re-building vignettes:
--- re-building ‘rxnat.Rmd’ using rmarkdown
Quitting from lines 133-135 (rxnat.Rmd) 
Error: processing vignette 'rxnat.Rmd' failed with diagnostics:
OpenSSL SSL_connect: Connection reset by peer in connection to nitrc.org:443 
--- failed re-building ‘rxnat.Rmd’

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

Error: Vignette re-building failed.
Execution halted
Error(s) in re-building vignettes:
  ...
--- re-building ‘rxnat.Rmd’ using rmarkdown
Quitting from lines 133-135 (rxnat.Rmd) 
Error: processing vignette 'rxnat.Rmd' failed with diagnostics:
gnutls_handshake() failed: Error in the pull function.
--- failed re-building ‘rxnat.Rmd’

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

Error: Vignette re-building failed.
Execution halted
Error(s) in re-building vignettes:
  ...
--- re-building ‘rxnat.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) not available. Falling back to R Markdown v1.
Quitting from lines 77-78 (rxnat.Rmd) 
Error: processing vignette 'rxnat.Rmd' failed with diagnostics:
Failed to connect to nitrc.org port 443: Operation timed out
--- failed re-building ‘rxnat.Rmd’

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

Error: Vignette re-building failed.
Execution halted