fix histogram2dcontour bins in mock

Author: archmoj

test/image/baselines/period_positioning2.png

@@ -158,13 +158,13 @@
             ],
             "xbins": {
                 "start": "2001-01-01",
-                "end": "2005-01-01",
-                "size": 31557600000
+                "end": "2004-12-31",
+                "size": 31536000000
             },
             "ybins": {
                 "start": "2001-01-01",
-                "end": "2005-01-01",
-                "size": 31557600000
+                "end": "2004-12-31",
+                "size": 31536000000
             },
             "xperiod": "M12",
             "xperiodalignment": "middle",