[#1085] Add dev dependency on serializer

Author: mickadoo

composer.json

@@ -33,7 +33,8 @@
         "knplabs/knp-paginator-bundle": "~2.4",
         "symfony/browser-kit" : "~2.3|~3.0",
         "symfony/expression-language" : "~2.4|~3.0",
-        "symfony/twig-bundle": "~2.3|~3.0"
+        "symfony/twig-bundle": "~2.3|~3.0",
+        "symfony/serializer": "~2.7|~3.0"
     },
     "autoload": {
         "psr-4": { "FOS\\ElasticaBundle\\": "" }