Fix start date in 1504

xzmeng · xzmeng · commit 868275ca2d73 · 2023-08-14T05:20:12.000+08:00
diff --git a/text/1504-int128.md b/text/1504-int128.md
@@ -1,5 +1,5 @@
 - Feature Name: int128
-- Start Date: 21-02-2016
+- Start Date: 2016-02-21
 - RFC PR: [rust-lang/rfcs#1504](https://github.com/rust-lang/rfcs/pull/1504)
 - Rust Issue: [rust-lang/rust#35118](https://github.com/rust-lang/rust/issues/35118)
 
