Use Str::wrap() instead of nesting Str::start() inside Str::finish() (#811)

Co-authored-by: Deeka Wong <8337659+huangdijia@users.noreply.github.com>

Author: huangdijia

src/Mailable/Headers.php

@@ -95,7 +95,7 @@ public function text(array $text)
     public function referencesString(): string
     {
         return collect($this->references)->map(function ($messageId) {
-            return Str::finish(Str::start($messageId, '<'), '>');
+            return Str::wrap($messageId, '<', '>');
         })->implode(' ');
     }
 }