fix diff command build error

[kazupon]

No description provided.

[codecov-io]

Codecov Report

Merging #54 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #54      +/-   ##
==========================================
+ Coverage    90.9%   90.92%   +0.01%     
==========================================
  Files           9        9              
  Lines         473      474       +1     
  Branches       56       56              
==========================================
+ Hits          430      431       +1     
  Misses         21       21              
  Partials       22       22

Impacted Files	Coverage Δ
src/commands/diff.ts	86.66% <100%> (+0.45%)	⬆️

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