fix default unit

[JaSei]

fix of #5

[codecov-io]

Codecov Report

Merging #6 into master will increase coverage by 8.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
+ Coverage   82.35%   90.38%   +8.03%     
==========================================
  Files           2        2              
  Lines          51       52       +1     
==========================================
+ Hits           42       47       +5     
+ Misses          8        5       -3     
+ Partials        1        0       -1

Impacted Files	Coverage Δ
retry.go	94.59% <100%> (+2.92%)	⬆️
options.go	80% <0%> (+20%)	⬆️

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