fix a typo

[wuxiangzhou2010]

No description provided.

[codecov]

Codecov Report

Merging #1366 into master will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1366      +/-   ##
==========================================
+ Coverage   75.67%   75.74%   +0.06%     
==========================================
  Files         262      262              
  Lines       11476    11476              
==========================================
+ Hits         8685     8693       +8     
+ Misses       1997     1991       -6     
+ Partials      794      792       -2

Impacted Files	Coverage Δ
common/serial/string.go	86.36% <ø> (ø)	⬆️
proxy/shadowsocks/ota.go	86.66% <0%> (-3.34%)	⬇️
common/log/logger.go	87.5% <0%> (-3.13%)	⬇️
app/dns/udpns.go	71.58% <0%> (-0.55%)	⬇️
proxy/shadowsocks/client.go	70% <0%> (+1%)	⬆️
common/mux/client.go	69.37% <0%> (+2.39%)	⬆️
common/mux/server.go	69.56% <0%> (+5.07%)	⬆️

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