Fix ci in plot_shift + doc improvements in bootstrap

[raphaelvallat]

Closes #259

• Several other doc improvements in preparation of pingouin v0.5.2

[codecov]

Codecov Report

Merging #282 (477a4d4) into master (1bc5a86) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #282      +/-   ##
==========================================
- Coverage   98.99%   98.99%   -0.01%     
==========================================
  Files          19       19              
  Lines        3294     3290       -4     
  Branches      527      527              
==========================================
- Hits         3261     3257       -4     
  Misses         17       17              
  Partials       16       16              

Impacted Files	Coverage Δ
pingouin/bayesian.py	100.00% <ø> (ø)
pingouin/pairwise.py	99.40% <ø> (ø)
pingouin/effsize.py	100.00% <100.00%> (ø)
pingouin/plotting.py	96.50% <100.00%> (ø)
pingouin/regression.py	100.00% <100.00%> (ø)

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