Could not use with Slim4
Hi,
I am trying to use this with Slim4 framwork and looks like after installing slim with [following setps](https://www.slimframework.com/docs/v4/start/installation.html),
I could not run `composer require cboden/ratchet`. I get the error
![image](https://user-images.githubusercontent.com/6584304/132134636-ebd88c44-0a20-4455-aa81-1231f9e94587.png)

Please help
