[Golang][client] fix RFC-3339 date-time query param

Created by: grokify

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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@antihax @bvwells

Description of the PR

Resubmitting https://github.com/OpenAPITools/openapi-generator/pull/325

I just used 3.1.0 to regenerate the go-ringcentral client and noticed that while this was previously merged, the issue persists in the release or master branch.

It was merged into 3.1.x and mentioned on release page, but did not get into the actual file.

• Release: https://github.com/OpenAPITools/openapi-generator/releases/tag/v3.1.0
• 3.1.0 File 100ec449: https://github.com/OpenAPITools/openapi-generator/blob/100ec449fe45176fc5479af078d02b80f855838c/modules/openapi-generator/src/main/resources/go/client.mustache