Minor fix needed in py.test message

When testing an affiliated package, the following message pops up

```
============================= test session starts ==============================
platform linux2 -- Python 2.7.3 -- pytest-2.3.3

Testing Astropy version 0.2.
Running tests in aplpy.
```

Maybe it should say ``Running tests using Astropy version 0.2`` instead of ``Testing Astropy version 0.2.``?

(don't have time to fix it right now, so if someone else gets to it first, feel free to fix)