Use existing key in fallback

Author: timacdonald

src/Illuminate/Cache/RateLimiting/Limit.php

@@ -150,6 +150,8 @@ public function response(callable $callback)
  */
  public function fallbackKey()
  {
- return "attempts:{$this->maxAttempts}:decay:{$this->decaySeconds}";
+ $prefix = $this->key === '' ? '' : "{$this->key}:";
+
+ return "{$prefix}attempts:{$this->maxAttempts}:decay:{$this->decaySeconds}";
  }
 }