I have a Symfony web app that needs to be upgraded from Symfony 2.6 to 3.4. Is there a standardized, bare bones `composer.json` that shows what's necessary for the current version? The demo app's file on github seems to be filled with a bunch of extra things that I'm not entirely sure I need. Ideally, I'd like to update the existing `composer.json` and put out backwards compatibility fires where they may pop up.

EDIT: my current composer is -

```
{
    "license": "Private",
    "type": "project",
    "description": "Home/e-commerce site",
    "autoload": {
        "psr-0": { "": "src/", "SymfonyStandard": "app/" }
    },
    "require": {
        "php": ">=5.3.3",
        "symfony/symfony": "2.6.*",
        "doctrine/orm": "~2.2,>=2.2.3",
        "doctrine/doctrine-bundle": "~1.2",
        "twig/extensions": "~1.0",
        "symfony/assetic-bundle": "2.6.*",
        "symfony/swiftmailer-bundle": "~2.3",
        "symfony/monolog-bundle": "~2.4",
        "sensio/distribution-bundle": "~3.0",
        "sensio/framework-extra-bundle": "~3.0",
        "incenteev/composer-parameter-handler": "~2.0",
        "jms/security-extra-bundle": "dev-master",
        "jms/di-extra-bundle": "dev-master",
        "friendsofsymfony/user-bundle": "2.0.*@dev",
        "roave/security-advisories": "dev-master"
    },
    "require-dev": {
        "sensio/generator-bundle": "~2.3"
    },
    "scripts": {
        "post-root-package-install": [
            "SymfonyStandard\\Composer::hookRootPackageInstall"
        ],
        "post-install-cmd": [
            "Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::removeSymfonyStandardFiles"
        ],
        "post-update-cmd": [
            "Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::removeSymfonyStandardFiles"
        ]
    },
    "config": {
        "bin-dir": "bin"
    },
    "extra": {
        "symfony-app-dir": "app",
        "symfony-web-dir": "web",
        "incenteev-parameters": {
            "file": "app/config/parameters.yml",
            "keep-outdated": true
        },
        "branch-alias": {
            "dev-master": "2.6-dev"
        }
    }
}

```