support redmine 4.1.1 and rails (5.2.4.2)

[tony1223]

The PR could work with following enviroment.

Redmine version 4.1.1.stable Ruby version 2.6.6-p146 (2020-03-31) [x86_64-linux] Rails version 5.2.4.2

BUT the following line which commented might be a bit risky, if someone got some time to fix this in strong parameters , it will be much better.

attr_accessible :is_done, :subject
attr_protected :id

I could leave this in my env. QQ