title: sequelize v5 using typescript, Type expected for model.d.ts file
body: <p>This is the error message I am getting after upgrading to V5 from V4. </p>
  
  <p>I can comment out the unknown part from the lib, and everything else runs just fine.</p>
  
  <blockquote>
    <p>node_modules/sequelize/types/lib/model.d.ts:108:29 - error TS1110:
    Type expected.</p>
    
    <p>108   method: string | [string, ...unknown[]];</p>
  </blockquote>
  
  <p>This is my typical model definition:</p>
  
  <pre><code>interface IAllergenExtend extends Model {
    id?: number;
    name: string;
    description: string;
    updatedAt?: string;
    createdAt?: string;
  }
  
  type AllergenModel = typeof Model &amp;
    (new (values?: object, options?: BuildOptions) =&gt; IAllergenExtend) &amp; {
      associate: (model: IDB) =&gt; any;
    };
  
  const allergenFactory = (sequalize: Sequelize) =&gt; {
    const Allergen = (&lt;AllergenModel&gt;sequalize.define('Allergen', {
      id: {
        allowNull: false,
        autoIncrement: true,
        primaryKey: true,
        type: DataTypes.INTEGER
      },
      name: {
        allowNull: false,
        type: DataTypes.TEXT
      },
      description: {
        allowNull: false,
        type: DataTypes.TEXT
      }
    })) as AllergenModel;
  
    Allergen.associate = (model: IDB) =&gt; {
      Allergen.belongsToMany(model.Dish, {
        through: db.AllergenDish,
        foreignKey: 'allergenId',
        as: 'dishes'
      });
    };
  
    return Allergen;
  };
  
  export { allergenFactory, AllergenModel };
  </code></pre>