Something I realise is your composer.json file will have some sort of script like 
"scripts": {
    "post-root-package-install": [
        "php -r \"copy('.env.example', '.env');\""
    ],
    "post-create-project-cmd": [
        "php artisan key:generate"
    ],
    "post-install-cmd": [
        "php artisan clear-compiled",
        "php artisan optimize"
    ],
    "pre-update-cmd": [
        "php artisan clear-compiled"
    ],
    "post-update-cmd": [
        "php artisan optimize"
    ],
    "post-autoload-dump": [
        "Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
        "@php artisan package:discover"
    ]
},
what works for me: 
"scripts": {
    "post-root-package-install": [
        "@php -r \"file_exists('.env') || copy('.env.example', '.env');\""
    ],
    "post-create-project-cmd": [
        "@php artisan key:generate"
    ],
    "post-autoload-dump": [
        "Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
        "@php artisan package:discover"
    ]
},
removing post install cmd helped running composer install without any issue.
Hope this helps
Cheers!!