Add punctuation to comment

Author: fredden

tests/Core/Config/SniffsExcludeArgsTest.php

@@ -136,7 +136,7 @@ public static function dataInvalidSniffs()
                 'suggestion' => 'Standard.Category.Sniff',
             ];
 
-            // Too many dots
+            // Too many dots.
             $data[$argument.'; error-code'] = [
                 'argument'   => $argument,
                 'value'      => 'Standard.Category.Sniff.Code.Extra',