Replaced "OpenAPI Generator 4.x.y" with "OpenAPI Generator 4+"

Author: jaaufauvre

README.md

@@ -755,7 +755,7 @@ ServiceApi serviceApi = new ServiceApi(client);
 // …
 ```
 
-##### Usage of the `OkHttpEncryptionInterceptor` (OpenAPI Generator 4.x.y)
+##### Usage of the `OkHttpEncryptionInterceptor` (OpenAPI Generator 4+)
 ```java
 ApiClient client = new ApiClient();
 client.setBasePath("https://sandbox.api.mastercard.com");