1.PHP artisan --version
2.vim vendor/laravel/framework/src/Illuminate/Foundation/Application.php
3：可以写在路由里
5.4版本的路由文件夹是routes。我们可以写在routesweb.php里。
Route::get('laravel-version', function(){
$laravel = app();
return "Your Laravel version is ".$laravel::VERSION;
});