I am creating my own slackbot. I decided to use project as a library to help me.
https://github.com/sagebind/slack-client/issues?utf8=%E2%9C%93&q=stability
i had the error in a symfony4 project with own bundles.
my-foo-bundle dev-master requires ramsey/uuid-doctrine ^1.5 -> satisfiable by ramsey/uuid-doctrine[1.5.0, 1.6.0] but these conflict with your requirements or minimum-stability.
the solution, i search for "ramsey/uuid-doctrine" in my bundles and i found different requirements "ramsey/uuid-doctrine ^1.5" (in my-foo-bundle) and "ramsey/uuid-doctrine dev-master" (in my app-configuration). So i delete the requirement in the app/composer.json.
This worked for me.