Error(s) in re-building vignettes:
  ...
--- re-building ‘learningtower_school.Rmd’ using rmarkdown
** Processing: /home/hornik/tmp/R.check/r-devel-gcc/Work/PKGS/learningtower.Rcheck/vign_test/learningtower/vignettes/learningtower_school_files/figure-html/unnamed-chunk-1-1.png
768x576 pixels, 3x8 bits/pixel, RGB
Input IDAT size = 23061 bytes
Input file size = 23163 bytes

Trying:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 20619
  zc = 9  zm = 8  zs = 1  f = 0
  zc = 1  zm = 8  zs = 2  f = 0
  zc = 9  zm = 8  zs = 3  f = 0
  zc = 9  zm = 8  zs = 0  f = 5
  zc = 9  zm = 8  zs = 1  f = 5
  zc = 1  zm = 8  zs = 2  f = 5
  zc = 9  zm = 8  zs = 3  f = 5
                               
Selecting parameters:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 20619

Output IDAT size = 20619 bytes (2442 bytes decrease)
Output file size = 20697 bytes (2466 bytes = 10.65% decrease)

trying URL 'https://github.com/kevinwang09/learningtower/raw/master/student_full_data/student_2018.rds'

Quitting from lines 90-117 [unnamed-chunk-2] (learningtower_school.Rmd)
Error: processing vignette 'learningtower_school.Rmd' failed with diagnostics:
cannot open URL 'https://github.com/kevinwang09/learningtower/raw/master/student_full_data/student_2018.rds'
--- failed re-building ‘learningtower_school.Rmd’

--- re-building ‘learningtower_student.Rmd’ using rmarkdown
** Processing: /home/hornik/tmp/R.check/r-devel-gcc/Work/PKGS/learningtower.Rcheck/vign_test/learningtower/vignettes/learningtower_student_files/figure-html/unnamed-chunk-2-1.png
768x576 pixels, 3x8 bits/pixel, RGB
Input IDAT size = 22149 bytes
Input file size = 22251 bytes

Trying:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 17795
  zc = 9  zm = 8  zs = 1  f = 0
  zc = 1  zm = 8  zs = 2  f = 0
  zc = 9  zm = 8  zs = 3  f = 0
  zc = 9  zm = 8  zs = 0  f = 5
  zc = 9  zm = 8  zs = 1  f = 5
  zc = 1  zm = 8  zs = 2  f = 5
  zc = 9  zm = 8  zs = 3  f = 5
                               
Selecting parameters:
  zc = 9  zm = 8  zs = 0  f = 0		IDAT size = 17795

Output IDAT size = 17795 bytes (4354 bytes decrease)
Output file size = 17873 bytes (4378 bytes = 19.68% decrease)

trying URL 'https://github.com/kevinwang09/learningtower/raw/master/student_full_data/student_2012.rds'

Quitting from lines 103-147 [unnamed-chunk-4] (learningtower_student.Rmd)
Error: processing vignette 'learningtower_student.Rmd' failed with diagnostics:
cannot open URL 'https://github.com/kevinwang09/learningtower/raw/master/student_full_data/student_2012.rds'
--- failed re-building ‘learningtower_student.Rmd’

SUMMARY: processing the following files failed:
  ‘learningtower_school.Rmd’ ‘learningtower_student.Rmd’

Error: Vignette re-building failed.
Execution halted