bump pg gem

Change-Id: I00d26eba514f8ced09cc0bfa42e8754e74e4ef69
Reviewed-on: https://gerrit.instructure.com/42284
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bryan Madsen <bryan@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>