Switch from SKS to Ubuntu keyserver

See also https://github.com/docker-library/faq#openpgp--gnupg-keys-and-verification and https://github.com/tianon/pgp-happy-eyeballs

Author: tianon

Dockerfile.template

@@ -237,7 +237,7 @@ RUN set -ex; \
 	curl -o /usr/local/bin/wp.gpg -fL "https://github.com/wp-cli/wp-cli/releases/download/v${WORDPRESS_CLI_VERSION}/wp-cli-${WORDPRESS_CLI_VERSION}.phar.gpg"; \
 	\
 	GNUPGHOME="$(mktemp -d)"; export GNUPGHOME; \
-	gpg --batch --keyserver ha.pool.sks-keyservers.net --recv-keys "$WORDPRESS_CLI_GPG_KEY"; \
+	gpg --batch --keyserver keyserver.ubuntu.com --recv-keys "$WORDPRESS_CLI_GPG_KEY"; \
 	gpg --batch --decrypt --output /usr/local/bin/wp /usr/local/bin/wp.gpg; \
 	gpgconf --kill all; \
 	rm -rf "$GNUPGHOME" /usr/local/bin/wp.gpg; unset GNUPGHOME; \