Prepare the 3.1.1 release

CHANGELOG

@@ -1,4 +1,4 @@
-# 3.1.1 (2020-XX-XX)
+# 3.1.1 (2020-10-27)
 
  * Fix "include(template_from_string())"
 

src/Environment.php

@@ -38,12 +38,12 @@ use Twig\TokenParser\TokenParserInterface;
  */
 class Environment
 {
-    const VERSION = '3.1.1-DEV';
+    const VERSION = '3.1.1';
     const VERSION_ID = 30101;
     const MAJOR_VERSION = 3;
     const MINOR_VERSION = 1;
     const RELEASE_VERSION = 1;
-    const EXTRA_VERSION = 'DEV';
+    const EXTRA_VERSION = '';
 
     private $charset;
     private $loader;