sqlite conflict_update version check ignores apsw version
Thanks for the quick fix! I had literally just hacked around my local install with the same monkeypatch:

```
import peewee
peewee.__sqlite_version__ = tuple(int(x) for x in apsw.sqlitelibversion().split('.'))
```
I'm using `APSWDatabase` with APSW 3.24.0, but calling `on_conflict` still raises an exception claiming 'ValueError: SQLite does not support specifying which values to preserve or update.' It appears that `conflict_update` is checking the Python sqlite3 module version, instead of the apsw sqlite version, when deciding whether or not the feature is supported.