Socket.gethostbyname deprecation warning

When requiring the agent gem, a deprecation warning is observed:

```
/usr/local/bundle/bundler/gems/instrumental_agent-ruby-e6b27a2199d2/lib/instrumental/agent.rb:18: warning: Socket.gethostbyname is deprecated; use Addrinfo.getaddrinfo instead.
```

Note: Observed with Ruby 3.0. Not known if this occurs on prior Ruby releases.