[aspnetcore] new keyword on ToJson Method when inherited from Dictionary

Created by: etherealjoy

Description

When a model is a map type and inherited from a dictionary the new keyword is added to ToJson method even when there is no accessible member to hide/override.

public partial class ResourceOperations : Dictionary<String, string>, 
    IEquatable<ResourceOperations>
{ 
    public  new string ToJson()

Warning	CS0109	The member 'ResourceOperations.ToJson()' does not hide an accessible member. 
The new keyword is not required.	

openapi-generator version

3.0.0

I detected this issue with old codebase. In current code base the map is not working.

OpenAPI declaration file content or url

  ResourceOperations:
    description: "An object describing the operations"
    type: "object"
    additionalProperties:
      type: "string"

Command line used for generation

java -jar ~/openapi-generator/modules/openapi-generator-cli/target/openapi-generator-cli.jar \
generate -i ./api.yaml -o ./genserver -l aspnetcore 

Suggest a fix/enhancement