Fix ROUNDUP and ROUNDDOWN for negative number

[n-longcape]

This is:

- [x] a bugfix
- [ ] a new feature

Checklist:

• Changes are covered by unit tests
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change
• Documentation is updated as necessary

Why this change is needed?

In relation to #1404.
I missed to fix ROUNDUP and ROUNDDOWN function in the case of negative number.
=ROUNDUP(4.4400,2) expected -4.44 but -4.45.
=ROUNDDOWN((-2.26 - 2.94),2) expected -5.2 but -5.19.

[PowerKiKi]

Thanks ! merged in f9f9f4c