[BUG] [Ruby] The generated Ruby client is using deprecated type `Fixnum`

Created by: autopp

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

The generated Ruby client is using Fixnum in YARD tag. Fixnum is deprecated in Ruby 2.4.0 and later (and integrated into Integer).

openapi-generator version

$ java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar version
4.0.0-SNAPSHOT

$ git log --oneline -n 1
ee75366051 (HEAD -> master, origin/master, origin/HEAD) Added proxy headers option for urllib3 (#2467)

OpenAPI declaration file content or url

N/A

Command line used for generation

N/A

Steps to reproduce

See:

• https://github.com/OpenAPITools/openapi-generator/blob/ee7536605152b6638bdab366eead347ea92748c2/modules/openapi-generator/src/main/resources/ruby-client/api_client.mustache#L39
• https://github.com/OpenAPITools/openapi-generator/blob/ee7536605152b6638bdab366eead347ea92748c2/samples/client/petstore/ruby/lib/petstore/api_client.rb#L47

Related issues/PRs

N/A

Suggest a fix

Use Integer instead of Fixnum. Integer is also available in versions below 2.4.0.