lib/classes/Service.js/Service/validate
class Service:  validate() {
    _.forEach(this.functions, (functionObj, functionName) => {
      if (!_.isArray(functionObj.events)) {
        throw new ServerlessError(`Events for "${functionName}" must be an array,` +
                          ` not an ${typeof functionObj.events}`);
      }
    });

    return this;
  }