relax `pg` dependency to allow both `0.17.x` and `0.18.x`. Closes #240.
relax `pg` dependency to allow both `0.17.x` and `0.18.x`. Closes #240.

/cc @jipiboily

clemensg/queue_classic,YodelTalk/queue_classic,QueueClassic/queue_classic,QueueClassic/queue_classic