Why does apt-get dist-upgrade change /usr/bin/ruby to /etc/alternatives/ruby?

Why does apt-get dist-upgrade change /usr/bin/ruby to /etc/alternatives/ruby?

When I run an apt-get update, apt-get dist-upgrade, the location of
/usr/bin/ruby changes from /usr/local/bin/ruby to /etc/alternatives/ruby.
This ends up breaking several cron jobs until I remember to correct it
back. Why is it doing this?
Thanks!