[SWIFT4] Generated Code has warnings when using Swift 4.2 Compiler

[james-rant]

Description

When using Xcode 10 with swift 4.2, the generated code from the swift4 openapi-generator contains a few warnings. They're not necessarily causing any problems, but I like a clean codebase.

The warnings:

APIs.swift:10:21: Static declarations are implicitly 'final'; use 'public' instead of 'open'
APIs.swift:13:21: Static declarations are implicitly 'final'; use 'public' instead of 'open'
APIs.swift:11:21: Static declarations are implicitly 'final'; use 'public' instead of 'open'
APIs.swift:12:21: Static declarations are implicitly 'final'; use 'public' instead of 'open'
Models.swift:18:14: 'let' properties are implicitly 'final'; use 'public' instead of 'open'
Models.swift:19:14: 'let' properties are implicitly 'final'; use 'public' instead of 'open'
Models.swift:20:14: 'let' properties are implicitly 'final'; use 'public' instead of 'open'
CodableHelper.swift:14:21: Static declarations are implicitly 'final'; use 'public' instead of 'open'
AlamofireImplementations.swift:157:141: Using '!' here is deprecated and will be removed in a future release
AlamofireImplementations.swift:359:141: Using '!' here is deprecated and will be removed in a future release

openapi-generator version

3.3.2

Command line used for generation

openapi-generator generate -i swagger.json -l swift4 -o ~/Desktop/APIClient

Steps to reproduce

• Generate a swift4 client from an open api spec document.
• Add the generated code to a Swift 4.2 project and build
• See warnings

Related issues/PRs

Swagger-Codegen has a related issue (which I also submitted a PR for before knowing about the OpenAPI-Generator fork) swagger-api/swagger-codegen#8336

Suggest a fix/enhancement

I will be submitting a PR to fix these warnings, and will update this issue when it's submitted.