python-flask server bug: Dashes in a header parameter should not be replaced with underscores

Description

The Swagger 2.0 specification allows header parameters with dashes (e.g., X-Request-ID), for example:
https://swagger.io/docs/specification/2-0/describing-parameters/

    get:
      summary: Checks if the server is alive.
      parameters:
        - in: header
          name: X-Request-ID
          type: string
          required: true

However, when I run the python-flask code generator, it replaces the dashes in the header parameter name with underscores (X_Request_ID):

    get:
      summary: "Checks if the server is alive."
      operationId: "status_get"
      parameters:
      - name: "X_Request_ID"
        in: "header"
        required: true
        type: "string"

Swagger-codegen version

2.3.1

Swagger declaration file content or url

Input:

swagger: "2.0"
info:
  description: ""
  version: "1.0.0"
  title: "Bug demo"
paths:
  /ping:
    get:
      summary: Checks if the server is alive.
      parameters:
        - in: header
          name: X-Request-ID
          type: string
          required: true
      responses:
        200:
          description: "success"
          schema:
            type: "string"

Generated output

---
swagger: "2.0"
info:
  description: ""
  version: "1.0.0"
  title: "Bug demo"
paths:
  /ping:
    get:
      summary: "Checks if the server is alive."
      operationId: "ping_get"
      parameters:
      - name: "X_Request_ID"
        in: "header"
        required: true
        type: "string"
      responses:
        200:
          description: "success"
          schema:
            type: "string"
      x-swagger-router-controller: "swagger_server.controllers.default_controller"
definitions: {}

Command line used for generation

N/A - I used the https://editor.swagger.io/ and selected Generate Server -> python-flask

Steps to reproduce

1. Copy the schema fragment from the
   https://swagger.io/docs/specification/2-0/describing-parameters/
   to the swagger editor
   https://editor.swagger.io/
2. Generate python-flask code (Generate Server -> python-flask)
3. Download the python-flask-server-generated.zip file and unzip it.
   Review python-flask-server\swagger_server\swagger\swagger.yaml
4. Observe that the header parameters name was changed.

Related issues/PRs

N/A

Suggest a fix/enhancement

N/A

Reproduce the issue in the python-flask server generator using the Swagger 2.0 header parameter example, then inspect the generated python-flask-server/swagger_server/swagger/swagger.yaml output. Compare the X-Request-ID input with the generated X_Request_ID value; done means the generated header parameter preserves its dashes.