bumped version to 2.3.1-DEV

CHANGELOG

@@ -1,3 +1,7 @@
+* 2.3.1 (2017-XX-XX)
+
+ * n/a
+
 * 2.3.0 (2017-03-22)
 
  * fixed a race condition handling when writing cache files

lib/Twig/Environment.php

@@ -16,12 +16,12 @@
  */
 class Twig_Environment
 {
-    const VERSION = '2.3.0';
-    const VERSION_ID = 20300;
+    const VERSION = '2.3.1';
+    const VERSION_ID = 20301;
     const MAJOR_VERSION = 2;
     const MINOR_VERSION = 3;
-    const RELEASE_VERSION = 0;
-    const EXTRA_VERSION = '';
+    const RELEASE_VERSION = 1;
+    const EXTRA_VERSION = 'DEV';
 
     private $charset;
     private $loader;