[JavaScript] Content-Type: application/json on GET(also HEAD,DELETE) requests

[noritama]

Description

The same problem as #476 is also occurring in javaScript.

openapi-generator version

master and 4.0.x

OpenAPI declaration file content or url

Use ping.yaml.

Command line used for generation

java -jar openapi-generator-cli.jar generate \
    -i ping.yaml \
    -l javascript \
    -o dist \
    -DuseES6=false \
    --additional-properties usePromises=true

Steps to reproduce

Generate client.

Related issues/PRs

#476

Suggest a fix/enhancement

Do not attempt to even infer a content type for a GET(also HEAD,DELETE) request.