prepared the 2.3.0 release

CHANGELOG

@@ -1,4 +1,4 @@
-* 2.3.0 (2017-XX-XX)
+* 2.3.0 (2017-03-22)
 
  * fixed a race condition handling when writing cache files
  * "length" filter now returns string length when applied to an object that does

lib/Twig/Environment.php

@@ -21,7 +21,7 @@ class Twig_Environment
     const MAJOR_VERSION = 2;
     const MINOR_VERSION = 3;
     const RELEASE_VERSION = 0;
-    const EXTRA_VERSION = 'DEV';
+    const EXTRA_VERSION = '';
 
     private $charset;
     private $loader;