Only update test domain

Use a more specific replacement pattern, otherwise we'll also update the email address, but an email with an IP and port number isn't valid and so the network isn't installed properly then.

See #1

travis.sh

@@ -20,7 +20,7 @@ install-wordpress() {
 	mysql -e 'CREATE DATABASE wordpress_test;' -uroot
 
 	# Configure WordPress for access through a web server.
-	sed -i "s/example.org/$WP_CEPT_SERVER/" wp-config.php
+	sed -i "s/'example.org'/'$WP_CEPT_SERVER'/" wp-config.php
 
 	# Install.
 	php tests/phpunit/includes/install.php wp-config.php "$WP_MULTISITE"