package redmine 3.4.4-1 failed to install/upgrade: installed redmine package post-installation script subprocess returned error exit status 7

Status changed to 'Confirmed' because the bug affects multiple users.

Server install of Ubuntu 18.04:

apt install redmine redmine-mysql ruby-fcgi

Here is the error messages:
Setting up redmine (3.4.4-1) ...
Determining localhost credentials from /etc/mysql/debian.cnf: succeeded.
dbconfig-common: writing config to /etc/dbconfig-common/redmine/instances/default.conf

Creating config file /etc/dbconfig-common/redmine/instances/default.conf with new version

Creating config file /etc/redmine/default/database.yml with new version
checking privileges on database redmine_default for redmine/instance@localhost: user creation needed.
granting access to database redmine_default for redmine/instance@localhost: success.
verifying access for redmine/instance@localhost: success.
creating database redmine_default: success.
verifying database redmine_default exists: success.
dbconfig-common: flushing administrative password
rake aborted!
Gem::LoadError: Specified 'mysql2' for database adapter, but the gem is not loaded. Add `gem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
/usr/share/redmine/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `eval'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `each'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
/var/lib/gems/2.5.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'

Caused by:
Gem::LoadError: can't activate mysql2 (>= 0.3.13, < 0.5), already activated mysql2-0.5.2. Make sure all dependencies are added to Gemfile.
/usr/share/redmine/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `eval'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `each'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
/var/lib/gems/2.5.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'
Tasks: TOP => db:migrate => environment
(See full trace by running task with --trace)
dpkg: error processing package redmine (--configure):
 installed redmine package post-installation script subprocess returned error exit status 1
Setting up ruby-sass-rails (5.0.6-1) ...
Setting up ruby-web-console (2.2.1-2) ...
Setting up ruby-turbolinks (2.5.3-3ubuntu1) ...
Errors were encountered while processing:
 redmine
E: Sub-process /usr/bin/dpkg returned an error code (1)