minor programming vignette fixes

[jangorecki]

closes #5538

[codecov]

Codecov Report

Merging #5432 (100ac6e) into master (2f67531) will increase coverage by 0.00%.
Report is 66 commits behind head on master.
The diff coverage is 100.00%.

❗ Current head 100ac6e differs from pull request most recent head ce7ddb6. Consider uploading reports for the commit ce7ddb6 to get more accurate results

@@           Coverage Diff           @@
##           master    #5432   +/-   ##
=======================================
  Coverage   99.51%   99.51%           
=======================================
  Files          78       80    +2     
  Lines       14756    14770   +14     
=======================================
+ Hits        14684    14698   +14     
  Misses         72       72           

Files	Coverage Δ
R/notin.R	100.00% <100.00%> (ø)
src/fread.c	99.41% <ø> (ø)
src/init.c	100.00% <ø> (ø)
src/negate.c	100.00% <100.00%> (ø)

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