Saving config needs root priviledges

[WhyNotHugo]

betty tries to save it's configuration globaly even if I'm not root, and, for course, it fails:

$ betty speak to me
/usr/lib/betty/config.rb:33:in `initialize': Permission denied @ rb_sysopen - /etc/betty/bettyconfig (Errno::EACCES)
        from /usr/lib/betty/config.rb:33:in `open'
        from /usr/lib/betty/config.rb:33:in `save'
        from /usr/lib/betty/config.rb:25:in `set'
        from /usr/lib/betty/config.rb:42:in `block in interpret'
        from /usr/bin/betty:89:in `call'
        from /usr/bin/betty:89:in `run'
        from /usr/bin/betty:202:in `main'
        from /usr/bin/betty:223:in `<main>'

$XDG_CONFIG_DIR should be used if UID != 0.