use proper inheritance

lib/dialects/mariadb/index.js

 'use strict';
 
-var MySQLDialect = require('../mysql');
+var MySQLDialect = require('../mysql')
+  , util = require('util');
 
 var MariaDialect = function(sequelize) {
   MySQLDialect.call(this, sequelize);
 };
 
-MariaDialect.prototype = MySQLDialect.prototype;
+util.inherits(MariaDialect, MySQLDialect);
 MariaDialect.prototype.name = 'mariadb';
 
 module.exports = MariaDialect;