fixed swiftmailer requirement in composer file

composer.json

@@ -19,7 +19,7 @@
         "php": ">=5.3.2",
         "doctrine/common": ">=2.1,<2.3-dev",
         "monolog/monolog": ">=1.0,<1.2-dev",
-        "swiftmailer/swiftmailer": ">=4.1.2,<4.2-dev",
+        "swiftmailer/swiftmailer": "4.2.*",
         "twig/twig": ">=1.1,<2.0-dev"
     },
     "replace": {