Update security.html.erb

Change reference to PCI DSS 4.0 to 4.0.1

Author: alanmaddrell

source/security.html.erb

@@ -38,7 +38,7 @@ title: Security and compliance
         <h2 class="govuk-heading-m">PCI compliance</h2>
 
         <p class="govuk-body">
-          GOV.UK&nbsp;Pay is certified as a level 1 service provider with the Payment Card Industry Data Security Standard (PCI DSS) version 4.0. The PCI DSS provides guidance to
+          GOV.UK&nbsp;Pay is certified as a level 1 service provider with the Payment Card Industry Data Security Standard (PCI DSS) version 4.0.1. The PCI DSS provides guidance to
           help maintain payment security.
         </p>