Turn updateDateTime into *Date.Update

date.go

@@ -24,6 +24,15 @@ func NewDate(t time.Time) *Date {
 	}
 }
 
+// Update updates the Date.
+func (d *Date) Update() {
+	if d == nil {
+		d = NewDate(time.Now())
+	} else {
+		d.DateTime = DateTime(time.Now())
+	}
+}
+
 // Check checks the Date for incompatibilities with RFC4287. It returns an
 // error.
 func (d *Date) Check() error {