Merge pull request #1877 from Tony133/docs/updateds-sequelize-v6

docs(sequelize): updateds sequelize v6.x

Author: kamilmysliwiec

content/recipes/sql-sequelize.md

@@ -68,7 +68,7 @@ In [Sequelize](https://github.com/sequelize/sequelize) the **Model** defines a t
 import { Table, Column, Model } from 'sequelize-typescript';
 
 @Table
-export class Cat extends Model<Cat> {
+export class Cat extends Model {
   @Column
   name: string;
 

content/techniques/sql.md

@@ -851,7 +851,7 @@ Sequelize implements the Active Record pattern. With this pattern, you use model
 import { Column, Model, Table } from 'sequelize-typescript';
 
 @Table
-export class User extends Model<User> {
+export class User extends Model {
   @Column
   firstName: string;
 
@@ -1036,7 +1036,7 @@ import { Column, Model, Table, HasMany } from 'sequelize-typescript';
 import { Photo } from '../photos/photo.model';
 
 @Table
-export class User extends Model<User> {
+export class User extends Model {
   @Column
   firstName: string;