Apply modernize suggestions

[AnnaShaleva]

Ref. nspcc-dev/.github#45.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.54%. Comparing base (77ecb0a) to head (9e6339b).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/generate/main.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #65      +/-   ##
==========================================
+ Coverage   27.50%   27.54%   +0.03%     
==========================================
  Files          20       20              
  Lines         778      777       -1     
==========================================
  Hits          214      214              
+ Misses        543      542       -1     
  Partials       21       21              

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