Git 2.18.3

Signed-off-by: Junio C Hamano <gitster@pobox.com>
(cherry picked from commit 21a3e5016bb218dc9b016284c88ba685bc446b70)
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
diff --git a/Documentation/RelNotes/2.18.3.txt b/Documentation/RelNotes/2.18.3.txt
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+Git v2.18.3 Release Notes
+=========================
+
+This release merges the security fix that appears in v2.17.4; see
+the release notes for that version for details.