PypiVersion version comparison must behave like packaging Version

```python
>>> from univers.versions import PypiVersion
>>> py_v1 = PypiVersion("1.11")
>>> py_v2 = PypiVersion("1.11.0")
>>> py_v1 == py_v2
False
>>> 
>>> 
>>> from packaging.version import Version
>>> pa_v1 = Version("1.11")
>>> pa_v2 = Version("1.11.0")
>>> pa_v1 == pa_v2
True
```