Connexion is broken with python 3.5

[ioggstream]

Reproduce

• run connexion with python 3.5

I expect

• code to be generated

Instead

• https://github.com/swagger-api/swagger-codegen/issues/7361

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\.
• [ ] Filed the PR against the correct branch: 3.0.0 branch for changes related to OpenAPI spec 3.0. Default: master.
• [ ] Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc)