Update AccountTransformer, tfw you confuse javascript and php operators

app/Transformer/Api/Mastodon/v1/AccountTransformer.php

@@ -11,7 +11,7 @@ class AccountTransformer extends Fractal\TransformerAbstract
 	{
 		$local = $profile->domain == null;
 		$is_admin = !$local ? false : $profile->user->is_admin;
-		$acct = $local ? $profile->username + '@' + config('pixelfed.domain.app') : substr($profile->username, 1);
+		$acct = $local ? $profile->username . '@' . config('pixelfed.domain.app') : substr($profile->username, 1);
 		$username = $local ? $profile->username : explode('@', $acct)[0];
 		return [
 			'id' => (string) $profile->id,