lib/classes/Service.js/Service/getEventInFunction
class Service:  getEventInFunction(eventName, functionName) {
    const event = this.getFunction(functionName).events.find(e => Object.keys(e)[0] === eventName);
    if (event) {
      return event;
    }
    throw new ServerlessError(`Event "${eventName}" doesn't exist in function "${functionName}"`);
  }