Lack of ASF header in some source file.

[ShannonDing]

1. Please describe the issue you observed:

   • What did you do (The steps to reproduce)?
     run license checker on the go native branch.
     java -jar apache-rat-0.12.jar rocketmq-client-go
   • What did you expect to see?
     All source files are under asf license header.
   • What did you see instead?
     8 source files are lack of asf header.

2. Please tell us about your environment:

   • What is your OS?
     macOS X 14
   • What is your client version?
     go native branch
   • What is your RocketMQ version?
     4.5.2

3. Other information (e.g. detailed explanation, logs, related issues, suggestions on how to fix, etc):
   Add the asf header for the source files.

---

Summary

Generated at: 2019-08-23T14:51:17+08:00

Notes: 3
Binaries: 3
Archives: 0
Standards: 109

Apache Licensed: 89
Generated Documents: 0

JavaDocs are generated, thus a license header is optional.
Generated files do not require license headers.

20 Unknown Licenses

---

Files with unapproved licenses:

../rocketmq-client-go/.gitignore
../rocketmq-client-go/.golangci.yml
../rocketmq-client-go/.travis.yml
../rocketmq-client-go/CONTRIBUTING.md
../rocketmq-client-go/PULL_REQUEST_TEMPLATE.md
../rocketmq-client-go/config.go
../rocketmq-client-go/go.mod
../rocketmq-client-go/go.sum
../rocketmq-client-go/release-notes.md
../rocketmq-client-go/consumer/offset_store_test.go
../rocketmq-client-go/consumer/statistics_test.go
../rocketmq-client-go/consumer/strategy_test.go
../rocketmq-client-go/docs/Introduction.md
../rocketmq-client-go/docs/client-design.gliffy
../rocketmq-client-go/docs/feature.md
../rocketmq-client-go/internal/mock_client.go
../rocketmq-client-go/internal/mock_namesrv.go
../rocketmq-client-go/internal/utils/net.go
../rocketmq-client-go/internal/utils/net_test.go
../rocketmq-client-go/internal/utils/string_test.go

---