Improvement on Error message 'pg_dump: aborting because of server version mismatch'
A customer ran into this problem. They're using RDS in AWS as their database.
```
2019-05-03 20:09:22 +0000 -- Dumping database ...
Dumping PostgreSQL database gitlab_production ... pg_dump: server version: 10.6; pg_dump version: 9.6.11
pg_dump: aborting because of server version mismatch
[FAILED]
rake aborted!
Backup::Error: Backup failed
/opt/gitlab/embedded/service/gitlab-rails/lib/backup/database.rb:50:in `dump'
/opt/gitlab/embedded/service/gitlab-rails/lib/tasks/gitlab/backup.rake:99:in `block (4 levels) in <top (required)>'
/opt/gitlab/embedded/service/gitlab-rails/lib/tasks/gitlab/backup.rake:10:in `block (3 levels) in <top (required)>'
/opt/gitlab/embedded/bin/bundle:23:in `load'
/opt/gitlab/embedded/bin/bundle:23:in `<main>'
Tasks: TOP => gitlab:backup:db:create
(See full trace by running task with --trace)
```
Now the error `pg_dump: aborting because of server version mismatch` is a bit vague.
What would “the server” be in this case? Would it be possible to extend the error message?
With something like `The version of pg_dump in the package does not match the version of the database`?
cc: @lbot @dblessing
issue