What version of phonenumbers is required?

Both locally and on [Travis](https://travis-ci.org/praekelt/ghr-mobi/jobs/15211238#L144) the build is failing because the required version of the `phonenumbers` package cannot be found. 

```
Downloading/unpacking phonenumbers (from app==0.0.1)
  Could not find a version that satisfies the requirement phonenumbers (from app==0.0.1) (from versions: 3.3a1, 3.5b1, 3.5b2, 3.7b1, 3.9b1, 4.0b1, 4.1b1, 4.2b1, 4.3b1, 4.4b1, 4.5b1, 4.6b1, 4.7b1, 4.8b1, 4.9b1, 5.0b1, 5.0b2, 5.1b1, 5.2b1, 5.3b1, 5.4b1, 5.5b1, 5.6b1, 5.7b1, 5.7b2, 5.8b1, 5.9b1, 3.3a1, 3.5b1, 3.5b2, 3.7b1, 3.9b1, 4.0b1, 4.1b1, 4.2b1, 4.3b1, 4.4b1, 4.5b1, 4.6b1, 4.7b1, 4.8b1, 4.9b1, 5.0b1, 5.0b2, 5.1b1, 5.2b1, 5.3b1, 5.4b1, 5.5b1, 5.6b1, 5.7b1, 5.7b2, 5.8b1, 5.9b1, 3.3a1, 3.5b1, 3.5b2, 3.7b1, 3.9b1, 4.0b1, 4.1b1, 4.2b1, 4.3b1, 4.4b1, 4.5b1, 4.6b1, 4.7b1, 4.8b1, 4.9b1, 5.0b1, 5.0b2, 5.1b1, 5.2b1, 5.3b1, 5.4b1, 5.5b1, 5.6b1, 5.7b1, 5.7b2, 5.8b1, 5.9b1, 3.3a1, 3.5b1, 3.5b2, 3.7b1, 3.9b1, 4.0b1, 4.1b1, 4.2b1, 4.3b1, 4.4b1, 4.5b1, 4.6b1, 4.7b1, 4.8b1, 4.9b1, 5.0b1, 5.0b2, 5.1b1, 5.2b1, 5.3b1, 5.4b1, 5.5b1, 5.6b1, 5.7b1, 5.7b2, 5.8b1, 5.9b1, 3.3a1, 3.5b1, 3.5b2, 3.7b1, 3.9b1, 4.0b1, 4.1b1, 4.2b1, 4.3b1, 4.4b1, 4.5b1, 4.6b1, 4.7b1, 4.8b1, 4.9b1, 5.0b1, 5.0b2, 5.1b1, 5.2b1, 5.3b1, 5.4b1, 5.5b1, 5.6b1, 5.7b1, 5.7b2, 5.8b1, 5.9b1, 3.3a1, 3.5b1, 3.5b2, 3.7b1, 3.9b1, 4.0b1, 4.1b1, 4.2b1, 4.3b1, 4.4b1, 4.5b1, 4.6b1, 4.7b1, 4.8b1, 4.9b1, 5.0b1, 5.0b2, 5.1b1, 5.2b1, 5.3b1, 5.4b1, 5.5b1, 5.6b1, 5.7b1, 5.7b2, 5.8b1, 5.9b1, 3.3a1, 3.5b1, 3.5b2, 3.7b1, 3.9b1, 4.0b1, 4.1b1, 4.2b1, 4.3b1, 4.4b1, 4.5b1, 4.6b1, 4.7b1, 4.8b1, 4.9b1, 5.0b1, 5.0b2, 5.1b1, 5.2b1, 5.3b1, 5.4b1, 5.5b1, 5.6b1, 5.7b1, 5.7b2, 5.8b1, 5.9b1)
```

What version does your `pip freeze` say you are on?