change the name of UnaryServerInterceptor's return

[catundercar]

req should be resp.Because interceptor is grpc.UnaryServerInterceptor

type UnaryServerInterceptor func(ctx context.Context, req interface{}, info *UnaryServerInfo, handler UnaryHandler) (resp interface{}, err error)

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[catundercar]

@googlebot I signed it!

[codecov-io]

Codecov Report

Merging #361 (cd635c9) into master (49f29dc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #361   +/-   ##
=======================================
  Coverage   72.81%   72.81%           
=======================================
  Files          41       41           
  Lines        1317     1317           
=======================================
  Hits          959      959           
  Misses        304      304           
  Partials       54       54           

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[johanbrandhorst]

LGTM

[johanbrandhorst]

Thanks for your contribution!