Debug string: don't make use of toStdString

toStdString  is not available in older versions of Qt

Change-Id: I6ddd9062deef5bafc8c0738f0d14cafcb0a7bfa7
Reviewed-by: Stepan Salenikovich <stepan.salenikovich@savoirfairelinux.com>
diff --git a/src/ringmainwindow.cpp b/src/ringmainwindow.cpp
index 5a969fa..b364fb9 100644
--- a/src/ringmainwindow.cpp
+++ b/src/ringmainwindow.cpp
@@ -1027,7 +1027,7 @@
     if (!accounts.isEmpty())
     {
         Account* account = accounts.first();
-        g_debug("Migrating account: %s", account->id().toStdString().c_str());
+        g_debug("Migrating account: %s", account->id().constData());
 
         GtkWidget* account_migration_view = account_migration_view_new(account);
         g_signal_connect_swapped(account_migration_view, "account-migration-completed", G_CALLBACK(handle_account_migrations), win);