pr2_ethercat_drivers: 1.8.4-0 in 'hydro/release.yaml' [bloom]

Increasing version of package(s) in repository `pr2_ethercat_drivers`:
- previous version: `1.8.3-0`
- new version: `1.8.4-0`
- distro file: `hydro/release.yaml`
- bloom version: `0.4.4`