Error(s) in re-building vignettes:
  ...
--- re-building ‘models-from-other.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
trying URL 'http://ryantimpe.com/files/mf_unicorn.PNG'
Content type 'image/png' length 277758 bytes (271 KB)
==================================================
downloaded 271 KB

Quitting from lines 34-41 (models-from-other.Rmd) 
Error: processing vignette 'models-from-other.Rmd' failed with diagnostics:
'where' must be an environment
--- failed re-building ‘models-from-other.Rmd’

--- re-building ‘models-from-program.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
Quitting from lines 33-48 (models-from-program.Rmd) 
Error: processing vignette 'models-from-program.Rmd' failed with diagnostics:
'where' must be an environment
--- failed re-building ‘models-from-program.Rmd’

--- re-building ‘models-from-tables.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
Quitting from lines 37-49 (models-from-tables.Rmd) 
Error: processing vignette 'models-from-tables.Rmd' failed with diagnostics:
'where' must be an environment
--- failed re-building ‘models-from-tables.Rmd’

--- re-building ‘models-piece-type.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
Quitting from lines 50-61 (models-piece-type.Rmd) 
Error: processing vignette 'models-piece-type.Rmd' failed with diagnostics:
'where' must be an environment
--- failed re-building ‘models-piece-type.Rmd’

--- re-building ‘mosaics.Rmd’ using rmarkdown
Warning in engine$weave(file, quiet = quiet, encoding = enc) :
  Pandoc (>= 1.12.3) and/or pandoc-citeproc not available. Falling back to R Markdown v1.
trying URL 'http://ryantimpe.com/files/mf_unicorn.PNG'
Content type 'image/png' length 277758 bytes (271 KB)
==================================================
downloaded 271 KB

Quitting from lines 29-36 (mosaics.Rmd) 
Error: processing vignette 'mosaics.Rmd' failed with diagnostics:
'where' must be an environment
--- failed re-building ‘mosaics.Rmd’

SUMMARY: processing the following files failed:
  ‘models-from-other.Rmd’ ‘models-from-program.Rmd’
  ‘models-from-tables.Rmd’ ‘models-piece-type.Rmd’ ‘mosaics.Rmd’

Error: Vignette re-building failed.
Execution halted