On `Issues` View, Sorting by `Due Soon` Should also Include Milestone Issues `Due Soon`

Version: GitLab CE 8.9.3

Currently, when I sort issues assigned to me by Due Soon it will only sort issues with an explicit due date assigned to them.

There is a separate option for sorting by Milestone due soon.

I think Due Soon should just subsume Milestone due soon as well, as all issues assigned to a milestone implicitly have a due date as well.