Make working directory compatible with macOS Catalina

[magneland]

Hello! I noticed that this gem uses '/' as its working directory here: [lib/daemons/daemonize.rb#L108]. In macOS Catalina this is a read-only directory, which causes issues. My understanding of the change in macOS Catalina is that it by default partitions the file system into read-only for the OS, and read-write for applications.

I hate to make a gem OS-specific, but maybe some kind of extra configuration might be possible?