prepared the 2.3.0 release

doc/changelog.rst

 Changelog
 =========
 
-2.3.0 (2018-XX-XX)
+2.3.0 (2018-04-20)
 ------------------
 
  * added support for defining users provider as a service ID

src/Silex/Application.php

@@ -41,7 +41,7 @@ use Silex\Provider\HttpKernelServiceProvider;
  */
 class Application extends Container implements HttpKernelInterface, TerminableInterface
 {
-    const VERSION = '2.3.0-DEV';
+    const VERSION = '2.3.0';
 
     const EARLY_EVENT = 512;
     const LATE_EVENT = -512;