fix Japanese format in date_format.dart

lib/src/date_format.dart

@@ -239,6 +239,8 @@ String formatDate(DateTime date, List<String> formats, LocaleType locale) {
         return formatDate(date, [D, ', ', dd, '. ', M], locale);
       } else if (locale == LocaleType.id) {
         return formatDate(date, [D, ', ', dd, ' ', M], locale);
+      } else if (locale == LocaleType.jp) {
+        return formatDate(date, [mm, '月', dd, '日', D], locale);
       } else {
         return formatDate(date, [D, ' ', M, ' ', dd], locale);
       }
@@ -253,6 +255,8 @@ String formatDate(DateTime date, List<String> formats, LocaleType locale) {
         return formatDate(date, [D, ', ', dd, '. ', M, ' ', yyyy], locale);
       } else if (locale == LocaleType.id) {
         return formatDate(date, [D, ', ', dd, ' ', M, ' ', yyyy], locale);
+      } else if (locale == LocaleType.jp) {
+        return formatDate(date, [yyyy, '年', mm, '月', dd, '日', D], locale);
       } else {
         return formatDate(date, [D, ' ', M, ' ', dd, ', ', yyyy], locale);
       }

lib/src/date_model.dart

@@ -324,7 +324,7 @@ class DatePickerModel extends CommonPickerModel {
   }
 
   String _localeYear() {
-    if (locale == LocaleType.zh) {
+    if (locale == LocaleType.zh || locale == LocaleType.jp) {
       return '年';
     } else if (locale == LocaleType.ko) {
       return '년';
@@ -334,7 +334,7 @@ class DatePickerModel extends CommonPickerModel {
   }
 
   String _localeMonth(int month) {
-    if (locale == LocaleType.zh) {
+    if (locale == LocaleType.zh || locale == LocaleType.jp) {
       return '$month月';
     } else if (locale == LocaleType.ko) {
       return '$month월';
@@ -345,7 +345,7 @@ class DatePickerModel extends CommonPickerModel {
   }
 
   String _localeDay() {
-    if (locale == LocaleType.zh) {
+    if (locale == LocaleType.zh || locale == LocaleType.jp) {
       return '日';
     } else if (locale == LocaleType.ko) {
       return '일';