Merge 1.8.1

[sjackman]

See https://github.com/Homebrew/brew/releases/tag/1.8.1

[codecov[bot]]

Codecov Report

Merging #875 into master will decrease coverage by 0.08%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #875      +/-   ##
==========================================
- Coverage   70.11%   70.02%   -0.09%     
==========================================
  Files         394      392       -2     
  Lines       21261    21339      +78     
==========================================
+ Hits        14907    14943      +36     
- Misses       6354     6396      +42

Impacted Files	Coverage Δ
cmd/desc.rb	73.07% <0%> (-18.59%)	:arrow_down:
dev-cmd/extract.rb	71.02% <0%> (-7.48%)	:arrow_down:
dev-cmd/test.rb	42.37% <0%> (-5.63%)	:arrow_down:
requirements/x11_requirement.rb	59.25% <0%> (-5.26%)	:arrow_down:
cleanup.rb	84.42% <0%> (-2.63%)	:arrow_down:
cache_store.rb	87.75% <0%> (-2.49%)	:arrow_down:
dependency_collector.rb	81.13% <0%> (-1.57%)	:arrow_down:
cli_parser.rb	94.24% <0%> (-0.5%)	:arrow_down:
download_strategy.rb	68.35% <0%> (-0.34%)	:arrow_down:
style.rb	87.25% <0%> (-0.25%)	:arrow_down:
... and 54 more

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