If you start to see something like this, e.g. on Heroku since they installed the postgres 9.5 client libraries on their dynos
/usr/lib/postgresql/9.5/bin/pg_dump: invalid option -- 'i'
Try "pg_dump --help" for more information.
rake aborted!
Error dumping database
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.4/lib/active_record/tasks/postgresql_database_tasks.rb:55:in `structure_dump'