修正了将时间导出到Excel文件中发生的错误

grmi/Date.go

@@ -39,3 +39,11 @@ func (self *Date) ToString() string {
 	date := self.Restore()
 	return date.Format(DateOutFormat)
 }
+
+func (self *Date) String() string {
+	if self == nil {
+		return ""
+	}
+	date := self.Restore()
+	return date.Format(DateTimeOutFormat)
+}

grmi/DateTime.go

@@ -39,3 +39,11 @@ func (self *DateTime) ToString() string {
 	date := self.Restore()
 	return date.Format(DateTimeOutFormat)
 }
+
+func (self *DateTime) String() string {
+	if self == nil {
+		return ""
+	}
+	date := self.Restore()
+	return date.Format(DateTimeOutFormat)
+}

grmi/Time.go

@@ -35,3 +35,11 @@ func (self *Time) ToString() string {
 	date := self.Restore()
 	return date.Format(TimeOutFormat)
 }
+
+func (self *Time) String() string {
+	if self == nil {
+		return ""
+	}
+	date := self.Restore()
+	return date.Format(DateTimeOutFormat)
+}