If you're doing this in RDS make sure to check what extensions each of your
databases in your RDS instance has (we use PostGIS and hstore for example)
and upgrade them incrementally. AWS provide the right libs installed to do
those updates between each engine version, but not necessarily between
engine versions more than 1 major version apart.
You can see which versions of the extensions are installed in RDS in each
engine version on this page:
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_PostgreSQL.html#PostgreSQL.Concepts.General.FeatureSupport.Extensions