milestone.rb

`NOW()` is a timestamp, with a maximum year (in Postgres) 294276 AD.

`milestones.due_date` is a date with a maximum year (again, in Postgres)
of 5874897 AD.

If there is a due date past the limit for the timestamp, comparing the
two will fail with:
    ERROR:  date out of range for timestamp

We also need to add validations to keep the due dates sensible, but for
now we can simply use `CURRENT_DATE` instead of `NOW()`, so the types
match with no coercion needed.