Fix generate-test-certs.sh script

Openssl does not take --subj parameter, but -subj.

Bug: 803774
Change-Id: Ie5e1da18941468fc66ea567134a49178b4260aba
Reviewed-on: https://chromium-review.googlesource.com/c/1370177Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Rob Buis <rbuis@igalia.com>
Cr-Commit-Position: refs/heads/master@{#615459}

third_party/blink/web_tests/external/wpt/signed-exchange/resources/generate-test-certs.sh

@@ -10,7 +10,7 @@ openssl ecparam -out 127.0.0.1.sxg.key -name prime256v1 -genkey
 openssl req -new -sha256 \
   -key 127.0.0.1.sxg.key \
   -out 127.0.0.1.sxg.csr \
-  --subj '/CN=127.0.0.1/O=Test/C=US'
+  -subj '/CN=127.0.0.1/O=Test/C=US'
 
 openssl x509 -req -days 3650 \
   -in 127.0.0.1.sxg.csr \