Add test case for Username

Author: arifszn

tests/Rules/UsernameTest.php

@@ -43,6 +43,7 @@ public function provider()
             [false, 'a b c'],
             [false, 'ｆｏｏbar'],
             [false, '😀'],
+            [false, 'john😀'],
         ];
     }
 }