not able to install in latest laravel-admin version

PHP version: 7.2 laravel version: 6.2 laravel-admin: 1.7.8

composer require laravel-admin-ext/config

Your requirements could not be resolved to an installable set of packages.

Problem 1

Conclusion: don't install laravel-admin-ext/config v1.0.3
Installation request for laravel/framework (locked at v6.6.1, required as ^6.2) -> satisfiable by laravel/framework[v6.6.1].
Conclusion: don't install laravel-admin-ext/config v1.0.2
Conclusion: don't install laravel-admin-ext/config v1.0.1
Can only install one of: encore/laravel-admin[1.5.x-dev, v1.7.8].
Can only install one of: encore/laravel-admin[v1.7.8, 1.5.x-dev].
Can only install one of: encore/laravel-admin[1.5.x-dev, v1.7.8].
laravel-admin-ext/config v1.0 requires encore/laravel-admin 1.5.* -> satisfiable by encore/laravel-admin[1.5.x-dev].
Installation request for laravel-admin-ext/config ^1.0 -> satisfiable by laravel-admin-ext/config[v1.0, v1.0.1, v1.0.2, v1.0.3].
Installation request for encore/laravel-admin (locked at v1.7.8, required as ^1.7) -> satisfiable by encore/laravel-admin[v1.7.8].

laravel-admin-extensions / config