Bump to v2.3.1

src/Mustache/Engine.php

@@ -23,7 +23,7 @@
  */
 class Mustache_Engine
 {
-    const VERSION        = '2.3.0';
+    const VERSION        = '2.3.1';
     const SPEC_VERSION   = '1.1.2';
 
     const PRAGMA_FILTERS = 'FILTERS';