why i am not getting option to upload the plugin in the wordpress site deployed using heroku code example

Example: add wordpress to heroku

//Docs
https://github.com/dzuelke/wordpress-12factor

//Steps
1- git clone -o upstream https://github.com/dzuelke/wordpress-12factor
2- cd wordpress-12factor
3- composer install
4- heroku apps:create websiteName
//Add your addons
5- heroku addons:create jawsdb/ heroku addons:create bucketeer/ heroku addons:create sendgrid
//Add at least heroku addons:create jawsdb to work
6- heroku config:set $(curl 'https://api.wordpress.org/secret-key/1.1/salt/' | sed -E -e "s/^define\('(.+)', *'(.+)'\);$/WORDPRESS_\1=\2/" -e 's/ //g')
7-git push heroku master
8- heroku run 'composer wordpress-setup-core-install -- --title="WordPress on Heroku" --admin_user=admin --admin_password=admin [email protected] --url="http://example.herokuapp.com/"'