"Required approvers" setting allows for negative numbers

Summary

• negative numbers are not acceptable for required approvers

Steps to reproduce

1. Navigate to a project => Secure => Policies => New policy => Scan Result Policy

Example Project

What is the current bug behavior?

Rule mode allows for a user to input a negative number

What is the expected correct behavior?

Rule mode does not allow for a user to input a negative number

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes