docs: fix License url

[popomore]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[codecov]

Codecov Report

Merging #10 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #10      +/-   ##
==========================================
- Coverage   95.69%   95.65%   -0.05%     
==========================================
  Files          12       12              
  Lines         186      184       -2     
==========================================
- Hits          178      176       -2     
  Misses          8        8

Impacted Files	Coverage Δ
app/lib/rotator.js	97.05% <0%> (-0.09%)	⬇️
app/schedule/clean_log.js	100% <0%> (ø)	⬆️

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[popomore]

eggjs/egg#989

[popomore]

• egg-logrotator@2.2.3