Anything older than 9.3 is unsupported by Postgres: https://www.postgresql.org/support/versioning/.
I don't think we should claim support in our module for unsupported versions,
particularly if we don't have CI on them.
Since we're *only* running CI on 9.2 at the moment, that's the safe claim
for our module support, even though it's already unsupported by Postgres.
See https://docs.travis-ci.com/user/database-setup/#using-a-different-postgresql-version
I'll raise a separate ticket about testing and supporting newer versions,
it's out of scope for this PR.
