Merge branch 'upgrade-brakeman' into 'master'

Upgrade Brakeman from 3.1.4 to 3.2.1

Includes support for Rails 5, bug fixes, and various additional vulnerability checks.

[See Changelog for more information](https://github.com/presidentbeef/brakeman/blob/master/CHANGES).

Working towards #14286.

See merge request !3397