Use JSONB by default on PostgreSQL
When Dict fields were added, not all the supported PostgreSQL version had the support for JSONB field. It was added in version 9.2 (which is now unsupported since November 9, 2017). I think it is time to use by default JSONB but we must keep support for existing column that are created as TEXT. Also this will prevent annoying migration warning between TEXT and JSONB when DB admin has modified the type.