erl_make_certs was removed from OTP in 20.1

Failures to copy this file are OK- for now. Later on a
better solution will have to be found.

Makefile

@@ -38,6 +38,9 @@ include erlang.mk
 DIALYZER_OPTS += --src -r test
 
 # Use erl_make_certs from the tested release during CI.
+#
+# Note that erl_make_certs was removed from OTP-20.1. For now
+# we are fine using the most recent version from OTP-20.
 
 ci-setup:: $(DEPS_DIR)/ct_helper
-	$(gen_verbose) cp ~/.kerl/builds/$(CI_OTP_RELEASE)/otp_src_git/lib/ssl/test/erl_make_certs.erl deps/ct_helper/src/
+	$(gen_verbose) cp ~/.kerl/builds/$(CI_OTP_RELEASE)/otp_src_git/lib/ssl/test/erl_make_certs.erl deps/ct_helper/src/ || true