Log Message:
databases/ruby-sequel: update to 5.19.0

=== 5.19.0 (2019-04-02)

* Use more optimized approach to merging hashes in ruby 2.5+ (jeremyevans)

* Use SQLite extended result codes when using ruby-sqlite3 1.4.0+ (jeremyevans)

* Recognize additional SQLite extended result codes in the shared sqlite adapter \ 
(jeremyevans)

* Add Database#rename_enum_value to the pg_enum extension (AlexWayfer) (#1603)

* Make Database#drop_table delete constraint validations metadata for that table \ 
if using the constraint_validations extension (jeremyevans)

* Speed up row fetching in the sqlite adapter (jeremyevans)

* Speed up row fetching and type conversion in the sqlanywhere adapter (jeremyevans)