Allow dot syntax when checking if a session has a value

Author: adamtomat

src/Session/Store.php

@@ -89,7 +89,7 @@ public function all()
 
     public function has($key)
     {
-        return Arr::exists($this->attributes, $key);
+        return Arr::has($this->attributes, $key);
     }
 
     public function pull($key)