Error(s) in re-building vignettes:
--- re-building 'intro-to-hypothesis-testing.Rmd' using rmarkdown
Quitting from lines 65-90 (intro-to-hypothesis-testing.Rmd) 
Error: processing vignette 'intro-to-hypothesis-testing.Rmd' failed with diagnostics:
there is no package called 'ggplot2'
--- failed re-building 'intro-to-hypothesis-testing.Rmd'

--- re-building 'one-sample-sign-tests.Rmd' using rmarkdown

Attaching package: 'distributions3'

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

    Gamma, quantile

The following object is masked from 'package:grDevices':

    pdf

--- finished re-building 'one-sample-sign-tests.Rmd'

--- re-building 'one-sample-t-confidence-interval.Rmd' using rmarkdown
Quitting from lines 93-138 (one-sample-t-confidence-interval.Rmd) 
Error: processing vignette 'one-sample-t-confidence-interval.Rmd' failed with diagnostics:
there is no package called 'ggplot2'
--- failed re-building 'one-sample-t-confidence-interval.Rmd'

--- re-building 'one-sample-t-test.Rmd' using rmarkdown
--- finished re-building 'one-sample-t-test.Rmd'

--- re-building 'one-sample-z-confidence-interval.Rmd' using rmarkdown
Quitting from lines 96-141 (one-sample-z-confidence-interval.Rmd) 
Error: processing vignette 'one-sample-z-confidence-interval.Rmd' failed with diagnostics:
there is no package called 'ggplot2'
--- failed re-building 'one-sample-z-confidence-interval.Rmd'

--- re-building 'one-sample-z-test-for-proportion.Rmd' using rmarkdown
--- finished re-building 'one-sample-z-test-for-proportion.Rmd'

--- re-building 'one-sample-z-test.Rmd' using rmarkdown
--- finished re-building 'one-sample-z-test.Rmd'

--- re-building 'paired-tests.Rmd' using rmarkdown
--- finished re-building 'paired-tests.Rmd'

--- re-building 'two-sample-z-test.Rmd' using rmarkdown
Quitting from lines 70-87 (two-sample-z-test.Rmd) 
Error: processing vignette 'two-sample-z-test.Rmd' failed with diagnostics:
there is no package called 'ggplot2'
--- failed re-building 'two-sample-z-test.Rmd'

SUMMARY: processing the following files failed:
  'intro-to-hypothesis-testing.Rmd'
  'one-sample-t-confidence-interval.Rmd'
  'one-sample-z-confidence-interval.Rmd' 'two-sample-z-test.Rmd'

Error: Vignette re-building failed.
Execution halted