prepared the 2.0.4 release

doc/changelog.rst

 Changelog
 =========
 
-2.0.4 (2016-XX-XX)
+2.0.4 (2016-11-06)
 ------------------
 
 * fixed twig.app_variable definition

src/Silex/Application.php

@@ -41,7 +41,7 @@ use Silex\Provider\HttpKernelServiceProvider;
  */
 class Application extends Container implements HttpKernelInterface, TerminableInterface
 {
-    const VERSION = '2.0.4-DEV';
+    const VERSION = '2.0.4';
 
     const EARLY_EVENT = 512;
     const LATE_EVENT = -512;