Should we drop PyMongo<3.5 support?

[ramnes]

http://api.mongodb.com/python/current/changelog.html#changes-in-version-3-5

Things that are modified in the pymongo-latest branch:

• [x] get_database rather than get_default_database
• [x] That logic with max_time_ms: https://github.com/numberly/mongo-thingy/blob/44e54fb306c4d8f6c26bc420dfe34c06f4a60ebf/mongo_thingy/__init__.py#L114-L115
• [x] Collection.count_documents instead of Cursor.count
• [x] insert_one, replace_one and delete_one instead of insert, update and remove

Fixed on PyMongo 3.5.0: https://github.com/mongodb/mongo-python-driver/commit/7b1cbace17348b71f49277d0edba7615b2da41d7

[Shir0kamii]

We made a branch called pymongo-latest which uses pymongo 3.7 and get rid of this logic.