Ruleset::explain(): use natural sorting

... for the list of included sniffs.

The `SORT_NATURAL` flag is available since PHP 5.4, so can be used.

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);
 
         ob_start();