ssh-tunnel port not being respected from config

Config
```
[database]
host = localhost
port = 5432
database = postgres
user = postgres

[ssh-tunnel]
host = localhost
port = 2222
user = vagrant
```

```bash
tern migrate
Unable to connect to PostgreSQL:
dial tcp 127.0.0.1:22: connect: connection refused
```

Would expect to see `127.0.0.1:2222` if the port was being used from the config. Using Mac if it matters.

```
tern version
tern v2.1.1
```

Start with the `tern migrate` entry point and reproduce the configuration shown in the issue. Trace how the `[ssh-tunnel]` port is read and verify that the connection target uses 2222 rather than 22. Done means the command connects to `127.0.0.1:2222` when that configuration is supplied.

Written by the indexing model from the issue text.