js/modules/k6: some lint fixes

[mstoykov]

works on #769

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d44ca21) 72.97% compared to head (816c8d1) 72.97%.

❗ Current head 816c8d1 differs from pull request most recent head 8ac4712. Consider uploading reports for the commit 8ac4712 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3563      +/-   ##
==========================================
- Coverage   72.97%   72.97%   -0.01%     
==========================================
  Files         280      280              
  Lines       20949    20949              
==========================================
- Hits        15288    15287       -1     
- Misses       4691     4692       +1     
  Partials      970      970              

Flag	Coverage Δ
macos	72.90% <ø> (?)
ubuntu	72.90% <ø> (-0.03%)	⬇️
windows	72.83% <ø> (+0.01%)	⬆️

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