doc: replace LKML link with lore.kernel.org

Since we're now recommending lore.kernel.org, replace LKML link
with lore.kernel.org.

Although LKML has been around for a long time, nothing lasts forever
(see Gmane). Since LKML uses opaque message identifiers, switching to
lore.kernel.org should be a strict improvement since, even if
lore.kernel.org goes down, the Message-ID will allow future readers to
look up the referenced messages on any other archive.

Signed-off-by: Denton Liu <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Denton-L

Documentation/technical/racy-git.txt

@@ -51,7 +51,7 @@ of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
 only fixes the issue for file systems with exactly 1 ns or 1 s
 resolution. Other file systems are still broken in current Linux
 kernels (e.g. CEPH, CIFS, NTFS, UDF), see
-https://lkml.org/lkml/2015/6/9/714
+https://lore.kernel.org/lkml/[email protected]/
 
 Racy Git
 --------