Added Sample_02_Serialized to composer samples (#834)

It was missing but it works.

There are also 3 Sample_12 files missing. But they do not work mainly because PhpPptTree does not exists.

Author: kw-pr

composer.json

@@ -42,6 +42,7 @@
         "samples": [
             "php samples/Sample_01_Complex.php",
             "php samples/Sample_01_Simple.php",
+            "php samples/Sample_02_Serialized.php",
             "php samples/Sample_03_Image.php",
             "php samples/Sample_03_Video.php",
             "php samples/Sample_04_Table.php",