README: update Chromium DEPS link

The HEAD psuedo ref always points to the default branch for us.

Change-Id: I02de777fbbb2883f15d111af05d722c40bb8c811
Reviewed-on: https://chromium-review.googlesource.com/c/linux-syscall-support/+/2532731
Reviewed-by: Mark Seaborn <mseaborn@chromium.org>
diff --git a/README.md b/README.md
index 70cbc85..b0cd129 100644
--- a/README.md
+++ b/README.md
@@ -130,7 +130,7 @@
 
 If you commit a change to LSS, please also commit a Chromium change to update
 `lss_revision` in
-[Chromium's DEPS](https://chromium.googlesource.com/chromium/src/+/master/DEPS)
+[Chromium's DEPS](https://chromium.googlesource.com/chromium/src/+/HEAD/DEPS)
 file.
 
 This ensures that the LSS change gets tested, so that people who commit later