Remove `upsert` option from save method.
Remove `upsert` option from save method.

coleifer/peewee,new-xiaji/peewee,py4a/peewee,teserak/peewee,coleifer/peewee,bopo/peewee,jarrahwu/peewee,new-xiaji/peewee,jnovinger/peewee,jarrahwu/peewee,jarrahwu/peewee,zhang625272514/peewee,fuzeman/peewee,zhang625272514/peewee,Sunzhifeng/peewee,Sunzhifeng/peewee,lez/peewee,coreos/peewee,fuzeman/peewee,ghukill/peewee,wenxer/peewee,jnovinger/peewee,wenxer/peewee,mackjoner/peewee,new-xiaji/peewee,coreos/peewee,zhang625272514/peewee,Sunzhifeng/peewee,stas/peewee,bopo/peewee,softside/peewee,ronyb29/peewee,bopo/peewee,coleifer/peewee,coreos/peewee