Ruleset::explain(): use natural sorting

... for the list of included sniffs.

The `SORT_NATURAL` and the `SORT_FLAG_CASE` flag are available since PHP 5.4, so can be used without issue.

src/Ruleset.php

@@ -238,7 +238,7 @@ public function __construct(Config $config)
     public function explain()
     {
         $sniffs = array_keys($this->sniffCodes);
-        sort($sniffs);
+        sort($sniffs, (SORT_NATURAL | SORT_FLAG_CASE));
 
         ob_start();