Charset content type identifier not supported

[zlaroche]

I've noticed that the source code doe does not properly register the response validator if an operation's content type is defined with the charset identifier, such as

content:
          application/json; charset=UTF-8:

The issue seems to be line 438 of node_modules/openapi-backend/validation.js, where it simply checks to see if the content is application/json, this missing an application/json with a charset identifier.

 const validator = this.getAjv(ValidationContext.Response);
        _.mapKeys(operation.responses, (res, status) => {
            const response = res;
            if (response.content && response.content['application/json'] && **response.content['application/json'].schema) {
                const validateFn = response.content['application/json'].schema;
                responseValidators[status] = validator.compile(validateFn);**
            }
            return null;
        });
        this.statusBasedResponseValidators[operationId] = responseValidators;

[LexLuengas]

As far as I can tell, neither the JSON spec nor the Media Type spec allow the usage of the "charset" parameter together with "application/json", so that would mean your example is part of an invalid OpenAPI document. For a better argumentation see axios/axios#2154 (comment) and request/request#383.