Fix argument name for inserting document

PyMongo uses the `document` parameter when updating a document. It uses `doc_or_docs` when inserting. With the introduction of `_update()` in 0205c73 I switched to named parameters instead of positional ones and failed to use the correct name for insertions.

I need to build more integration tests.
Update release date

The 0.4 release is being done early to address a critical bug in 0.3 which was fixed in d322d53.