Surprisingly painless upgrade to Twig 3.x.

composer.json

@@ -1,10 +1,9 @@
 {
     "require": {
-        "twig/twig": "^2.0",
+        "twig/twig": "^3.0",
         "swiftmailer/swiftmailer": "~6.0",
         "erusev/parsedown": "~1.6",
         "geoip2/geoip2": "~2.0",
-        "twig/extensions": "^1.5",
         "jublonet/codebird-php": "^3.1",
         "chillerlan/php-qrcode": "^3.0",
         "whichbrowser/parser": "^2.0"
@@ -21,6 +20,9 @@
         ]
     },
     "config": {
-        "preferred-install": "dist"
+        "preferred-install": "dist",
+        "allow-plugins": {
+            "composer/installers": true
+        }
     }
 }