Upgrade Redmine/Rails to mitigate CVE-2019-5418

See:

• https://github.com/mpgn/CVE-2019-5418
• https://weblog.rubyonrails.org/2019/3/13/Rails-4-2-5-1-5-1-6-2-have-been-released/

bugs.alpinelinux.org:

alpine-bugs:/usr/share/webapps/redmine# gem list --local '^rails$'

*** LOCAL GEMS ***

rails (4.2.8)

This should be updated to 4.2.11.1 at least.

(from redmine: issue id 10149, created on 2019-03-22)