Fix typo in Translator code comment

Fixes perfroming => performing

src/Illuminate/Translation/Translator.php

@@ -118,7 +118,7 @@ public function has($key, $locale = null, $fallback = true)
         $locale = $locale ?: $this->locale;
 
         // We should temporarily disable the handling of missing translation keys
-        // while perfroming the existence check. After the check, we will turn
+        // while performing the existence check. After the check, we will turn
         // the missing translation keys handling back to its original value.
         $handleMissingTranslationKeys = $this->handleMissingTranslationKeys;