This method is deprecated or moved on the latest stable version.
The last existing version (v4.0.2) is shown here.
version()
private
Returns the version
of the connected MySQL server.
# File activerecord/lib/active_record/connection_adapters/mysql_adapter.rb, line 555
def version
@version ||= @connection.server_info.scan(/^(\d+)\.(\d+)\.(\d+)/).flatten.map { |v| v.to_i }
end