Abstract factory (#366)

* rewrite of the Abstract Factory pattern

* update composer deps

* fixed argument to json_encode which cannot be null

Creational/AbstractFactory/UnixWriterFactory.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace DesignPatterns\Creational\AbstractFactory;
+
+class UnixWriterFactory implements WriterFactory
+{
+    public function createCsvWriter(): CsvWriter
+    {
+        return new UnixCsvWriter();
+    }
+
+    public function createJsonWriter(): JsonWriter
+    {
+        return new UnixJsonWriter();
+    }
+}