feat(config): add grpc config.

[appleboy]

fix #254

[codecov-io]

Codecov Report

Merging #255 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #255      +/-   ##
==========================================
+ Coverage   95.86%   95.87%   +0.01%     
==========================================
  Files          16       16              
  Lines        1160     1163       +3     
==========================================
+ Hits         1112     1115       +3     
  Misses         39       39              
  Partials        9        9

Impacted Files	Coverage Δ
gorush/server_unix.go	100% <100%> (ø)	⬆️
config/config.go	100% <100%> (ø)	⬆️

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