Use astroid version older than 1.3.0.

### Problem
`astroid`'s latest version (`1.3.0`) has [a bug](https://bitbucket.org/logilab/astroid/issue/55/astroid-130-explodes-on-import-pytest#comment-None) in the import processing system. This causes the build to [fail](https://travis-ci.org/OpenBazaar/OpenBazaar/builds/41562507) with an unexpected error. The error is actually a false positive:
```bash
(env)renelvon @ merchant ~/Repos/OpenBazaar (keep_astroid_back) % python2
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from pysqlcipher.dbapi2 import OperationalError
>>> 
```

### Temporary solution
Force use of astroid version `1.2.1`, the latest version prior to `1.3.0` and the one we have been using (implicitly) until today.

### Long term solution
Once the astroid team releases a bugfix, we should delete the `astroid<1.3.0` line from the test requirements.

### Note
This affects all 3 branches of the project, but since we are about to release `0.3.1`, we should fix it just here; it will be fixed on `master` once we release and on `develop` once we backmegre.