Bump version number and add upgrade script.

config.xml

@@ -2,11 +2,11 @@
 <module>
     <name>contactform</name>
     <displayName><![CDATA[Contact form]]></displayName>
-    <version><![CDATA[4.0.0]]></version>
+    <version><![CDATA[4.1.0]]></version>
     <description><![CDATA[Description for contact form module]]></description>
     <author><![CDATA[PrestaShop]]></author>
     <tab><![CDATA[front_office_features]]></tab>
     <is_configurable>0</is_configurable>
     <need_instance>1</need_instance>
 	<limited_countries></limited_countries>
-</module>
+</module>

contactform.php

@@ -55,7 +55,7 @@ public function __construct()
         $this->name = 'contactform';
         $this->author = 'PrestaShop';
         $this->tab = 'front_office_features';
-        $this->version = '4.0.0';
+        $this->version = '4.1.0';
         $this->bootstrap = true;
 
         parent::__construct();

upgrade/Upgrade-4.1.0.php

@@ -0,0 +1,34 @@
+<?php
+/*
+* 2007-2017 PrestaShop
+*
+* NOTICE OF LICENSE
+*
+* This source file is subject to the Academic Free License (AFL 3.0)
+* that is bundled with this package in the file LICENSE.txt.
+* It is also available through the world-wide-web at this URL:
+* http://opensource.org/licenses/afl-3.0.php
+* If you did not receive a copy of the license and are unable to
+* obtain it through the world-wide-web, please send an email
+* to [email protected] so we can send you a copy immediately.
+*
+* DISCLAIMER
+*
+* Do not edit or add to this file if you wish to upgrade PrestaShop to newer
+* versions in the future. If you wish to customize PrestaShop for your
+* needs please refer to http://www.prestashop.com for more information.
+*
+*  @author PrestaShop SA <[email protected]>
+*  @copyright  2007-2015 PrestaShop SA
+*  @license    http://opensource.org/licenses/afl-3.0.php  Academic Free License (AFL 3.0)
+*  International Registered Trademark & Property of PrestaShop SA
+*/
+
+if (!defined('_PS_VERSION_')) {
+    exit;
+}
+
+function upgrade_module_4_1_0($object)
+{
+    return $object->registerHook('registerGDPRConsent');
+}