I used to install and do:
$ sudo yum install -y postgresql94-server postgresql94
$ pg_dump -h name-of-db.us-east-1.rds.amazonaws.com -U user dbName > dump
You can actually install a newer version of Postgres with the Amazon Extras Library: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/amazon-linux-ami-basics.html#extras-library
I needed Postgres 10, so for me the command was:
sudo amazon-linux-extras install postgresql10
You can view a list of extras Amazon Linux provides by using this command:
amazon-linux-extras list