5.6.8

[BUG_FIX] Changes  \Swagger namespace to \OpenApi (#158)

* [BUG_FIX] Changes  \Swagger namespace to \OpenApi

- Last update on https://github.com/zircote/swagger-php changes  \Swagger namespace to \OpenApi
- Also annotations prefix changed from @OAS to @OA.

* Update annotations for testing - @OAS -> @OA

* Is OpenApi validation

* Removes else

* Styles fixing

* StyleCI fixes

* StyleCI suggestions

* StyleCI updates.