text: 
  exports.up = function(knex) {
    return knex.schema
        .createTable('users', table => {
           table.increments();
  
           table.string('username');
           table.string('password_digest');
           table.string('user_role').defaultTo('user');
           table.string('avatar');
  
           table.unique(['username']);
  
           table.timestamps();
        });
  };
  
  exports.down = function(knex) {
      return knex.schema
          .table('users', table => {
              table.dropUnique(['username']);
          })
          .dropTable('users');
  };
  