Correct cache key for single site, single sitemap

Signed-off-by: Marty Friedel <[email protected]>

src/Support/Sitemapamic.php

@@ -83,7 +83,7 @@ public function getCacheKeys()
                     ->toArray();
             } else {
                 // just return the key
-                return [$key];
+                return [$key.'.'.Site::default()];
             }
         } elseif ($mode === 'multiple') {
             // get the loaders