databases/ruby-sequel: update to 5.16.0

=== 5.16.0 (2019-01-02)

* Convert integer columns to bigint columns when copying SQLite databases to other databases using bin/sequel -C (jeremyevans) (#1584)

* Use nicer error messages for missing or empty migration directories (Lavode) (#1585)

* Make alter table emulation work correctly in SQLite 3.26.0+ (jeremyevans) (#1582)

* Do not unset new one_to_one associated objects' reciprocal associations before saving associated objects in the nested_attributes plugin (jeremyevans)

* Do not validate new one_to_one associated objects twice when saving in the nested_attributes plugin (jeremyevans)

* Fix :qualify_tables option to class_table_inheritance plugin to work correctly with subclasses of subclasses (benalavi) (#1581)

* Make class_table_inheritance plugin use the schema cache instead of sending a query to get columns for tables (kenaniah) (#1580)

* Remove loading of mysqlplus in the mysql adapter (jeremyevans)

* Make mysql adapter work correctly on ruby 2.6+ (jeremyevans)

* Add Database#rollback_on_exit to rollback transactions instead of committing them when exiting the transaction block (jeremyevans)

* Enable window functions in SQLite 3.26.0+ (jeremyevans)

* Do not override existing methods when creating Sequel::Model attribute getter/setter methods (jeremyevans) (#1578)

* Use parentheses for expressions being subscripted (e.g. (array_agg(column))[1]) (jeremyevans)

(taca)