relloc/python3: fix PyYAML package name
relloc/python3: fix PyYAML package name

On Fedora 29 (Scylla official toolchain uses it),
PyYAML package name is "python3-pyyaml", no uppercase character.

scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla