"name": "VENDOR/MODULENAME",
    "description": "description",
    "require": {
        "php": "~5.5.0|~5.6.0|~7.0.0"
    },
    "type": "magento2-module",
    "url": "git@bitbucket.org:VENDOR/MODULENAME.git",
    "version": "0.1.0",
    "license": [
        "OSL-3.0",
        "AFL-3.0"
    ],
    "extra": {
        "map": [
            [
                "*",
                "VENDOR/MODULENAME"
            ]
        ]
    },
   "autoload": {
    "files": [
        "registration.php"
    ],
    "psr-4": {
      "VENDOR\MODULENAME\": ""
    }
  }
}

{
        "type": "vcs",
        "url": "git@bitbucket.org:VENDOR/MODULENAME.git"
}

composer require VENDOR/MODULENAME

sudo php bin/magento setup:upgrade

Autoload error: Module 'VENDOR_MODULENAME' from '/var/www/html/magento2/sites/magento2_test3/app/code/VENDOR/MODULENAME' has been already defined in '/var/www/html/magento2/sites/magento2_test3/vendor/VENDOR/MODULENAME'