Fix typing problem

[ariesclark]

import { Service } from 'moleculer-decorators';
import HttpGateway from "moleculer-web";

@Service()
export default class HttpService {
    mixins = [HttpGateway]
}

Public property 'mixins' of exported class has or is using name 'ApiGatewayErrors' from external module "moleculer-web" but cannot be named.
Public property 'mixins' of exported class has or is using name 'IncomingRequest' from external module "moleculer-web" but cannot be named.
Public property 'mixins' of exported class has or is using name 'GatewayResponse' from external module "moleculer-web" but cannot be named.

This pull request exposes the required interfaces for this to work.

[0x0a0d]

Hi, you can try my pull #259

[icebob]

259 covers it.