fix: minValue/maxValue intput/output types

[Sec-ant]

Before:

After:

Fixes #266.

[Sec-ant]

I just noticed value, notValue and equal validations have similar type problems like this. I wonder if this fix is the right direction, so I can try to fix those validations, too. @fabian-hiller

Updated: I pushed a new commit to fix them all. Please review my code.

[fabian-hiller]

Thank you! I will review your changes in the next days.

[fabian-hiller]

I will first check to see if the issue #266 still exists after we change our API to this proposal: #463

[fabian-hiller]

I think this was solved with #502