add trailing slash

Signed-off-by: Jessica Frazelle <acidburn@docker.com>

hack/release.sh

@@ -289,7 +289,7 @@ EOF
 # Upload the index script
 release_index() {
 	echo "Releasing index"
-	url="$(s3_url)" hack/make.sh install-script
+	url="$(s3_url)/" hack/make.sh install-script
 	write_to_s3 "s3://$BUCKET_PATH/index" < "bundles/$VERSION/install-script/install.sh"
 }