Make `driver: :chrome` work again

[jmuheim]

See http://stackoverflow.com/questions/29387097/capybara-and-chrome-driver-sqlite3busyexception-database-is-locked.

# To make chrome driver work, we need to monkey patch active record, otherwise we get an "SQLite3::BusyException: database is locked". See http://stackoverflow.com/questions/29387097.
class ActiveRecord::Base
  mattr_accessor :shared_connection
  @@shared_connection = nil

  def self.connection
    @@shared_connection || retrieve_connection
  end
end
ActiveRecord::Base.shared_connection = ActiveRecord::Base.connection