py-peewee: updated to 3.6.4

3.6.4:
Take a whole new approach, following what simplejson does. Allow the
build_ext command class to fail, and retry without extensions in the event we
run into issues building extensions.

3.6.3:
Add check in setup.py to determine if a C compiler is available before
building C extensions.

3.6.2:
Use ctypes.util.find_library to determine if libsqlite3 is installed.
Should fix problems people are encountering installing when SQLite3 is not
available.

3.6.1:
Fixed issue with setup script.

3.6.0:
* Support for Python 3.7, including bugfixes related to new StopIteration
  handling inside of generators.
* Support for specifying ROWS or RANGE window frame types.
* Add APIs for user-defined window functions if using [pysqlite3](https://github.com/coleifer/pysqlite3)
  and sqlite 3.25.0 or newer.
* TimestampField now uses 64-bit integer data-type for storage.
* Added support to pwiz and playhouse.reflection to enable generating
  models from VIEWs.
* Added lower-level database API for introspecting VIEWs.
* Revamped continuous integration setup for better coverage, including 3.7 and
  3.8-dev.
* Allow building C extensions even if Cython is not installed, by distributing
  pre-generated C source files.
* Switch to using setuptools for packaging.


(adam)