Log Message:
databases/py-peewee: Update to 3.5.0.

Backwards-incompatible changes
- Custom Model repr no longer use the convention of overriding
  __unicode__, and now use __str__.
- Redesigned the sqlite json1 integration and changed some of the APIs
  and semantics of various JSONField methods.

New features
- Better default repr for model classes and fields.
- ForeignKeyField() accepts a new initialization parameter,
  deferrable, for specifying when constraints should be enforced.
- BitField.flag() can be called without a value parameter for the
  common use-case of using flags that are powers-of-2.
- SqliteDatabase pragmas can be specified as a dict (previously
  required a list of 2-tuples).
- SQLite TableFunction (docs) will print Python exception tracebacks
  raised in the initialize and iterate callbacks, making debugging
  significantly easier.

Bug fixes
- Fixed bug in migrator.add_column() where, if the field being added
  declared a non-standard index type (e.g., binary json field with GIN
  index), this index type was not being respected.
- Fixed bug in database.table_exists() where the implementation did
  not match the documentation.
- Fixed bug in SQLite TableFunction implementation which raised errors
  if the return value of the iterate() method was not a tuple.