Listen's use of Digest::MD5 breaks support on FIPS enabled machines

Please review usage of Digest::MD5 and migrate to a different hash algorithm that is not disabled in when FIPS is enabled.

```
$ rails server
=> Booting Puma
=> Rails 5.2.1 application starting in development
=> Run `rails server -h` for more startup options
md5_dgst.c(78): OpenSSL internal error, assertion failed: Digest MD5 forbidden in FIPS mode!
Aborted
```
