This PR addresses #1015
Starting from Rails version 5.0.2 the default serializer of PostgreSQL columns returns an ActiveRecord::ConnectionAdapters::PostgreSQL::OID::Array object instead of a string. This new object is not suitable for JSON encoding and breaks versioning of any array fields backed by Postgres.
Whenever a PostgreSQL array is used, instead of asking Active Record for a serializer we introduce our own, which simply returns the underlying array without any modifications.
Jared Beck