Package suggested but not available for checking: 'RGtk2'
Error(s) in re-building vignettes:
  ...
--- re-building 'IntroductionToGFD.Rmd' using rmarkdown
Quitting from lines 106-107 (IntroductionToGFD.Rmd) 
Error: processing vignette 'IntroductionToGFD.Rmd' failed with diagnostics:
The GUI cannot be used without packages RGtk2.
--- failed re-building 'IntroductionToGFD.Rmd'

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

Error: Vignette re-building failed.
Execution halted
Package suggested but not available for checking: ‘RGtk2’
Error(s) in re-building vignettes:
  ...
--- re-building ‘IntroductionToGFD.Rmd’ using rmarkdown
Quitting from lines 106-107 (IntroductionToGFD.Rmd) 
Error: processing vignette ‘IntroductionToGFD.Rmd’ failed with diagnostics:
The GUI cannot be used without packages RGtk2.
--- failed re-building ‘IntroductionToGFD.Rmd’

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

Error: Vignette re-building failed.
Execution halted
Package suggested but not available for checking: ‘RGtk2’
Error(s) in re-building vignettes:
--- re-building ‘IntroductionToGFD.Rmd’ using rmarkdown
Quitting from lines 106-107 (IntroductionToGFD.Rmd) 
Error: processing vignette 'IntroductionToGFD.Rmd' failed with diagnostics:
The GUI cannot be used without packages RGtk2.
--- failed re-building ‘IntroductionToGFD.Rmd’

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

Error: Vignette re-building failed.
Execution halted
Package suggested but not available for checking: ‘RGtk2’
Error(s) in re-building vignettes:
--- re-building ‘IntroductionToGFD.Rmd’ using rmarkdown
Quitting from lines 106-107 (IntroductionToGFD.Rmd) 
Error: processing vignette 'IntroductionToGFD.Rmd' failed with diagnostics:
The GUI cannot be used without packages RGtk2.
--- failed re-building ‘IntroductionToGFD.Rmd’

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

Error: Vignette re-building failed.
Execution halted
Package suggested but not available for checking: 'RGtk2'
Error(s) in re-building vignettes:
--- re-building 'IntroductionToGFD.Rmd' using rmarkdown
Quitting from lines 106-107 (IntroductionToGFD.Rmd) 
Error: processing vignette 'IntroductionToGFD.Rmd' failed with diagnostics:
The GUI cannot be used without packages RGtk2.
--- failed re-building 'IntroductionToGFD.Rmd'

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

Error: Vignette re-building failed.
Execution halted
Package suggested but not available for checking: ‘RGtk2’
Error(s) in re-building vignettes:
  ...
--- re-building ‘IntroductionToGFD.Rmd’ using rmarkdown
Quitting from lines 106-107 (IntroductionToGFD.Rmd) 
Error: processing vignette 'IntroductionToGFD.Rmd' failed with diagnostics:
The GUI cannot be used without packages RGtk2.
--- failed re-building ‘IntroductionToGFD.Rmd’

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

Error: Vignette re-building failed.
Execution halted
Package suggested but not available for checking: ‘RGtk2’
Error(s) in re-building vignettes:
  ...
--- re-building ‘IntroductionToGFD.Rmd’ using rmarkdown
Quitting from lines 106-107 (IntroductionToGFD.Rmd) 
Error: processing vignette 'IntroductionToGFD.Rmd' failed with diagnostics:
The GUI cannot be used without packages RGtk2.
--- failed re-building ‘IntroductionToGFD.Rmd’

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

Error: Vignette re-building failed.
Execution halted
Package suggested but not available for checking: ‘RGtk2’
Error(s) in re-building vignettes:
  ...
--- re-building ‘IntroductionToGFD.Rmd’ using rmarkdown
Quitting from lines 106-107 (IntroductionToGFD.Rmd) 
Error: processing vignette 'IntroductionToGFD.Rmd' failed with diagnostics:
The GUI cannot be used without packages RGtk2.
--- failed re-building ‘IntroductionToGFD.Rmd’

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

Error: Vignette re-building failed.
Execution halted