I have found a solution that works on Ubuntu.
My mistake was that had not installed the my-sql
library before trying to connect.
Please follow these steps to do this. Run the following commands:
sudo apt-get install mysql-client libmysqlclient-dev
sudo gem install mysql2
Add the following to the gemfile
gem 'mysql2', '~> 0.3.15'
And then run:
bundle install