refactor: msg key first char must be lower

Author: adhocore

src/Asserts.php

@@ -59,7 +59,7 @@ public function assertAll(array $expectations, $actual, array $messages = [])
                 $assert = 'assert' . ucfirst($assert);
             }
 
-            $msgKey = \str_replace('assert', '', $assert);
+            $msgKey = \lcfirst(\str_replace('assert', '', $assert));
 
             $this->{$assert}($expected, $actual, $messages[$assert] ?? $messages[$msgKey] ?? null);
         }