Changed the due_date format in Card

YYYY-MM-DD was the chosen format due to the original intention
observed in def set_due, which was different from 'self.due' assignment
in Card.fetch.  For practical reasons, YYYY-MM-DD was chosen.

- Due date of Card is in YYYY-MM-DD format.
- Extra test case was added for set_due on a card.

test/test_trello.py

@@ -1,6 +1,7 @@
 from trello import TrelloClient
 import unittest
 import os
+import datetime
 
 class TrelloClientTestCase(unittest.TestCase):
 
@@ -126,6 +127,37 @@ def test51_add_card(self):
 		if not card:
 			self.fail("No card created")
 
+	def test52_add_card_set_due(self):
+		boards = self._trello.list_boards()
+		board_id = None
+		for b in boards:
+			if b.name != os.environ['TRELLO_TEST_BOARD_NAME']:
+				continue
+
+			for l in b.open_lists():
+				try:
+					name = "Testing from Python"
+					description = "Description goes here"
+					card = l.add_card(name, description)
+				except Exception as e:
+					print str(e)
+					self.fail("Caught Exception adding card")
+
+                                # Set the due date to be 3 days from now
+                                today = datetime.datetime.today()
+                                day_detla = datetime.timedelta(3)
+                                due_date = today + day_detla #
+                                card.set_due(due_date)
+                                expected_due_date = card.due
+                                # Refresh the due date from cloud
+                                card.fetch()
+                                actual_due_date = card.due[:10]
+                                self.assertEquals(expected_due_date, actual_due_date)
+				break
+			break
+		if not card:
+			self.fail("No card created")
+
 def suite():
 	tests = ['test01_list_boards', 'test10_board_attrs', 'test20_add_card']
 	return unittest.TestSuite(map(TrelloClientTestCase, tests))

trello/__init__.py

@@ -519,7 +519,8 @@ def fetch(self):
         self.idBoard = json_obj['idBoard']
         self.labels = json_obj['labels']
         self.badges = json_obj['badges']
-        self.due = json_obj['due']
+        # For consistency, due date is in YYYY-MM-DD format
+        self.due = json_obj.get('due', '')[:10]
         self.checked = json_obj['checkItemStates']
 
         self.checklists = []