Fix subject transaltion

Author: Imaginaerum

app/design/frontend/Magento/luma/Magento_Customer/email/account_new.html

@@ -4,7 +4,7 @@
  * See COPYING.txt for license details.
  */
 -->
-<!--@subject Welcome to {{var store.getFrontendName()}} @-->
+<!--@subject {{trans "Welcome to %store_name" store_name=$store.getFrontendName()}} @-->
 <!--@vars {
 "var this.getUrl($store, 'customer/account/')":"Customer Account URL",
 "var customer.email":"Customer Email",