Fix config-related warning

I haven't investigated yet, but there is a deprecation warning appearing by default which we should probably fix:

```
In [1]: import astropy

In [2]: astropy.test()
WARNING: AstropyDeprecationWarning: Config parameter 'auto_colname' in section [astropy.table.column] is deprecated. Use 'auto_colname' in section [astropy.table] instead. [astropy.config.configuration]
============================= test session starts ==============================
```