Fix Changelog entry

Rename a Changelog.d file, so that it gets picked up as expected by
scripts/assemble_changelog.py.

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/ChangeLog.d/remove_allow_sha1_in_certificates b/ChangeLog.d/remove_allow_sha1_in_certificates.txt
similarity index 100%
rename from ChangeLog.d/remove_allow_sha1_in_certificates
rename to ChangeLog.d/remove_allow_sha1_in_certificates.txt