add skip serialization for opt value

src/requests/restrict_chat_member.rs

@@ -22,6 +22,7 @@ pub struct RestrictChatMember<'a> {
     ///Date when restrictions will be lifted for the user, unix time. If user
     /// is restricted for more than 366 days or less than 30 seconds from the
     /// current time, they are considered to be restricted forever
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub until_date: Option<u64>,
 }