Update issue number to point to tracking issue

Author: yungcomputerchair

library/std/src/net/tcp.rs

@@ -499,7 +499,7 @@ impl TcpStream {
     /// let stream = TcpStream::connect("127.0.0.1:8080")
     ///                        .expect("Couldn't connect to the server...");
     /// stream.set_keepalive(true).expect("set_keepalive call failed");
-    #[unstable(feature = "tcp_keepalive", issue = "69774")]
+    #[unstable(feature = "tcp_keepalive", issue = "155889")]
     pub fn set_keepalive(&self, keepalive: bool) -> io::Result<()> {
         self.0.set_keepalive(keepalive)
     }
@@ -520,7 +520,7 @@ impl TcpStream {
     /// stream.set_keepalive(true).expect("set_keepalive call failed");
     /// assert_eq!(stream.keepalive().unwrap_or(false), true);
     /// ```
-    #[unstable(feature = "tcp_keepalive", issue = "69774")]
+    #[unstable(feature = "tcp_keepalive", issue = "155889")]
     pub fn keepalive(&self) -> io::Result<bool> {
         self.0.keepalive()
     }