support pulling rate limit from the user instance

Author: taylorotwell

src/Illuminate/Routing/Middleware/ThrottleRequests.php

@@ -75,6 +75,10 @@ protected function resolveMaxAttempts($request, $maxAttempts)
             $maxAttempts = explode('|', $maxAttempts, 2)[$request->user() ? 1 : 0];
         }
 
+        if (! is_numeric($maxAttempts) && $request->user()) {
+            $maxAttempts = $request->user()->{$maxAttempts};
+        }
+
         return (int) $maxAttempts;
     }