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

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Quitting from lines 17-20 (anova.Rmd) 
Error: processing vignette 'anova.Rmd' failed with diagnostics:
there is no package called 'devtools'
--- failed re-building 'anova.Rmd'

--- re-building 'chi_squared.Rmd' using rmarkdown

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Quitting from lines 17-20 (chi_squared.Rmd) 
Error: processing vignette 'chi_squared.Rmd' failed with diagnostics:
there is no package called 'devtools'
--- failed re-building 'chi_squared.Rmd'

--- re-building 'infer.Rmd' using rmarkdown

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Quitting from lines 34-36 (infer.Rmd) 
Error: processing vignette 'infer.Rmd' failed with diagnostics:
there is no package called 'devtools'
--- failed re-building 'infer.Rmd'

--- re-building 'observed_stat_examples.Rmd' using rmarkdown

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Quitting from lines 27-29 (observed_stat_examples.Rmd) 
Error: processing vignette 'observed_stat_examples.Rmd' failed with diagnostics:
there is no package called 'devtools'
--- failed re-building 'observed_stat_examples.Rmd'

--- re-building 't_test.Rmd' using rmarkdown

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Quitting from lines 17-20 (t_test.Rmd) 
Error: processing vignette 't_test.Rmd' failed with diagnostics:
there is no package called 'devtools'
--- failed re-building 't_test.Rmd'

SUMMARY: processing the following files failed:
  'anova.Rmd' 'chi_squared.Rmd' 'infer.Rmd'
  'observed_stat_examples.Rmd' 't_test.Rmd'

Error: Vignette re-building failed.
Execution halted