DatePicker: fix bug for wrong year number when week cross the year like 2014/12/29

packages/date-picker/src/picker.vue

@@ -162,8 +162,14 @@ const TYPE_VALUE_RESOLVER_MAP = {
   },
   week: {
     formatter(value, format) {
-      let date = formatDate(value, format);
-      const week = getWeekNumber(value);
+      let week = getWeekNumber(value);
+      let month = value.getMonth();
+      const trueDate = new Date(value);
+      if (week === 1 && month === 11) {
+        trueDate.setHours(0, 0, 0, 0);
+        trueDate.setDate(trueDate.getDate() + 3 - (trueDate.getDay() + 6) % 7);
+      }
+      let date = formatDate(trueDate, format);
 
       date = /WW/.test(date)
             ? date.replace(/WW/, week < 10 ? '0' + week : week)