[BUG][GO] generated go code not not formatted properly

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• • generated sample code in ./samples/client/petstore/go/
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• • branch master date 2019-10-02 commit c136b83bdb5e56ddb297de7f0d5bb9af447a9e54
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• • run go fmt on the generated code and view changes via git diff
• [Optional] Bounty to sponsor the fix (example)

Description

The generated code does not follow the go coding standards (go fmt)

openapi-generator version

commit c136b83bdb5e56ddb297de7f0d5bb9af447a9e54 (latest commit on master on 2019-10-02T15:27:00)

Steps to reproduce

cd ./samples/client/petstore/go
cd ./go-petstore
go fmt ./*
cd ../go-petstore-withXml
go fmt ./*
cd ../../../../server/petstore/go-gin-api-server
go fmt ./*

Suggest a fix

Correct all mustache templates and add a test for the build servers which runs "go fmt" and checks if there are any changed files. If yes, the test should fail.

Start in samples/client/petstore/go/ and server/petstore/go-gin-api-server, then run the listed go fmt commands and inspect the resulting git diff. Trace the generated output back to the Go mustache templates. Done means the generated samples require no formatting changes and a build-server test fails when go fmt would modify files.