Update to laravel 5.6 from 5.5 composer fails - php

Question

I've been following the upgrade guide provided on the Laravel website from 5.5 -> 5.6
https://laravel.com/docs/5.6/upgrade
When I run composer install everything seems okay, but then I run composer update everything gets wonky, this seems to be something I should be concerned about, how do I fix it?
Your requirements could not be resolved to an installable set of packages.
Problem 1
- Installation request for orchestra/testbench 3.6.2 -> satisfiable by orchestra/testbench[v3.6.2].
- Conclusion: don't install laravel/framework v5.6.7
- Conclusion: don't install laravel/framework v5.6.6
- sofa/eloquence v5.5.1 requires sofa/eloquence-base 5.5.* -> satisfiable by sofa/eloquence-base[v5.5].
- sofa/eloquence v5.5.1 requires sofa/eloquence-base 5.5.* -> satisfiable by sofa/eloquence-base[v5.5].
- sofa/eloquence-base v5.5 requires illuminate/database 5.5.* -> satisfiable by laravel/framework[v5.5.19], illuminate/database[v5.5.0, v5.5.16, v5.5.17, v5.5.2, v5.5.28, v5.5.33, v5.5.34, v5.5.35, v5.5.36].
- sofa/eloquence-base v5.5 requires illuminate/database 5.5.* -> satisfiable by laravel/framework[v5.5.19], illuminate/database[v5.5.0, v5.5.16, v5.5.17, v5.5.2, v5.5.28, v5.5.33, v5.5.34, v5.5.35, v5.5.36].
- don't install laravel/framework v5.6.4|remove laravel/framework v5.5.19
- don't install illuminate/database v5.5.0|don't install laravel/framework v5.6.4
- don't install illuminate/database v5.5.16|don't install laravel/framework v5.6.4
- don't install illuminate/database v5.5.17|don't install laravel/framework v5.6.4
- don't install illuminate/database v5.5.2|don't install laravel/framework v5.6.4
- don't install illuminate/database v5.5.28|don't install laravel/framework v5.6.4
- don't install illuminate/database v5.5.33|don't install laravel/framework v5.6.4
- don't install illuminate/database v5.5.34|don't install laravel/framework v5.6.4
- don't install illuminate/database v5.5.35|don't install laravel/framework v5.6.4
- don't install illuminate/database v5.5.36|don't install laravel/framework v5.6.4
- orchestra/testbench v3.6.2 requires laravel/framework ~5.6.4 -> satisfiable by laravel/framework[v5.6.4, v5.6.5, v5.6.6, v5.6.7].
- Conclusion: don't install laravel/framework v5.6.5
- Installation request for sofa/eloquence ~5.5.1 -> satisfiable by sofa/eloquence[v5.5.1].
Here is what my composer file looks like
{
"name": "laravel/laravel",
"description": "The Laravel Framework.",
"keywords": ["framework", "laravel"],
"license": "MIT",
"type": "project",
"require": {
"php": ">=5.6.4",
"laravel/framework": "5.6.*",
"ext-ldap": "*",
"tymon/jwt-auth": "0.5.*",
"adldap2/adldap2-laravel": "3.0.*",
"barryvdh/laravel-cors": "*",
"regulus/activity-log": "0.5.*",
"backup-manager/laravel": "^1.2.2",
"league/flysystem-sftp": "^1.0",
"intervention/image": "^2.3",
"sofa/eloquence": "~5.5.1",
"sofa/eloquence-base":"~5.5",
"shiftonelabs/laravel-nomad": "^1.0",
"predis/predis": "^1.1",
"shiftonelabs/laravel-cascade-deletes": "^1.0",
"kalnoy/nestedset": "^4.3",
"laravel/tinker": "^1.0",
"guzzlehttp/guzzle": "~6.0",
"pusher/pusher-php-server": "~3.0",
"swiftmailer/swiftmailer":"^6.0",
"fideloper/proxy":"~4.0"
},
"require-dev": {
"laravel/dusk": "~2.0.0",
"fzaninotto/faker": "~1.4",
"mockery/mockery": "0.9.*",
"phpunit/phpunit": "~7.0",
"filp/whoops": "~2.0",
"orchestra/testbench":"3.6.2",
"symfony/css-selector": "3.1.*",
"symfony/dom-crawler": "3.1.*",
"laracasts/generators": "dev-master as 1.1.4",
"barryvdh/laravel-ide-helper": "^2.4"
},
"autoload": {
"classmap": [
"database"
],
"psr-4": {
"App\\": "app/"
}
},
"autoload-dev": {
"psr-4": {
"Tests\\": "tests/"
}
},
"scripts": {
"post-root-package-install": [
"php -r \"file_exists('.env') || copy('.env.example', '.env');\""
],
"post-create-project-cmd": [
"php artisan key:generate"
],
"post-install-cmd": [
"Illuminate\\Foundation\\ComposerScripts::postInstall",
"php artisan optimize"
],
"post-update-cmd": [
"Illuminate\\Foundation\\ComposerScripts::postUpdate",
"php artisan ide-helper:generate",
"php artisan ide-helper:meta",
"php artisan optimize"
],"post-autoload-dump": [
"Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
"#php artisan package:discover"
]
},
"config": {
"preferred-install": "dist",
"optimize-autoloader": true
},
"extra": {
"laravel": {
"dont-discover": [
"laravel/dusk"
]
}
}
}

Answer 1

It looks like sofa/eloquence 5.5.1 requires Laravel 5.5, which is preventing your upgrade to Laravel 5.6.
It looks like they released a package three days ago to be compatible with Laravel 5.6; you can edit your composer file to change its version to 5.6 and run composer update.
"sofa/eloquence": "^5.6",
"sofa/eloquence-base":"^5.6",

Answer 2

As per documentation says:
Laravel 5.6 requires PHP 7.1.3 or higher.
Try to change your composer.json with:
"require": {
"php": ">=7.1.3",
Let me know if it helps
EDIT
try to change the config:
"config": {
"preferred-install": "dist",
"sort-packages": true,
"optimize-autoloader": true,
"minimum-stability":"dev",
"prefer-stable": true
}
and check if all the required plugins support the latest version of laravel.