COIL: Migrate master to HEAD

Update links still pointing to master, update to point to HEAD

BUG=b:224796805
TEST=navigate to updated link and/or N/A

Change-Id: I881d9ee433ae6cfc9195f69d6e24c93843fd238e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/frecon/+/3525497
Tested-by: Jonathon Murphy <jpmurphy@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Owners-Override: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Jonathon Murphy <jpmurphy@google.com>
diff --git a/common.mk b/common.mk
index aed7d3e..02757ae 100644
--- a/common.mk
+++ b/common.mk
@@ -7,7 +7,7 @@
 #
 # NOTE NOTE NOTE
 #  The authoritative common.mk is located in:
-#    https://chromium.googlesource.com/chromiumos/platform2/+/master/common-mk
+#    https://chromium.googlesource.com/chromiumos/platform2/+/HEAD/common-mk
 #  Please make all changes there, then copy into place in other repos.
 # NOTE NOTE NOTE
 #