Add missing require 'set'

[avdv]

Fixes #371

Description

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• Relevant Issues : colorls --git-status crashes with traceback #371
• Relevant PRs : (none)
• Type of change :
  • New feature
  • Bug fix for existing feature
  • Code quality improvement
  • Addition or Improvement of tests
  • Addition or Improvement of documentation

[codecov-commenter]

Codecov Report

Merging #372 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #372      +/-   ##
==========================================
+ Coverage   88.02%   88.04%   +0.02%     
==========================================
  Files           8        8              
  Lines         501      502       +1     
==========================================
+ Hits          441      442       +1     
  Misses         60       60              

Impacted Files	Coverage Δ
lib/colorls/git.rb	73.33% <100.00%> (+0.91%)	⬆️

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[xbjfk]

I applied this patch, and the crash was gone. Thank you :)