[PHP] Upgrade php-cs-fixer to 2.12, enables PHP >= 7.2 support (#769)

* upgrade php-cs-fixer to 2.12

* ran petstore-security-test for php

* updating openapi3 php petstore example

samples/client/petstore-security-test/php/lib/Model/ModelInterface.php

@@ -0,0 +1,96 @@
+<?php
+/**
+ * ModelInterface
+ *
+ * PHP version 5
+ *
+ * @category Class
+ * @package  OpenAPI\Client\Model
+ * @author   OpenAPI Generator team
+ * @link     https://openapi-generator.tech
+ */
+
+/**
+ * OpenAPI Petstore *_/ ' \" =end -- \\r\\n \\n \\r
+ *
+ * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\  *_/ ' \" =end --
+ *
+ * OpenAPI spec version: 1.0.0 *_/ ' \" =end -- \\r\\n \\n \\r
+ * Contact: something@something.abc *_/ ' \" =end -- \\r\\n \\n \\r
+ * Generated by: https://openapi-generator.tech
+ * OpenAPI Generator version: 3.2.1-SNAPSHOT
+ */
+
+/**
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech
+ * Do not edit the class manually.
+ */
+
+namespace OpenAPI\Client\Model;
+
+/**
+ * Interface abstracting model access.
+ *
+ * @package OpenAPI\Client\Model
+ * @author  OpenAPI Generator team
+ */
+interface ModelInterface
+{
+    /**
+     * The original name of the model.
+     *
+     * @return string
+     */
+    public function getModelName();
+
+    /**
+     * Array of property to type mappings. Used for (de)serialization
+     *
+     * @return array
+     */
+    public static function openAPITypes();
+
+    /**
+     * Array of property to format mappings. Used for (de)serialization
+     *
+     * @return array
+     */
+    public static function openAPIFormats();
+
+    /**
+     * Array of attributes where the key is the local name, and the value is the original name
+     *
+     * @return array
+     */
+    public static function attributeMap();
+
+    /**
+     * Array of attributes to setter functions (for deserialization of responses)
+     *
+     * @return array
+     */
+    public static function setters();
+
+    /**
+     * Array of attributes to getter functions (for serialization of requests)
+     *
+     * @return array
+     */
+    public static function getters();
+
+    /**
+     * Show all the invalid properties with reasons.
+     *
+     * @return array
+     */
+    public function listInvalidProperties();
+
+    /**
+     * Validate all the properties in the model
+     * return true if all passed
+     *
+     * @return bool
+     */
+    public function valid();
+}