Allow twig2 (#1205)

I _think_ this will allow Twig2, but am not sure if it should be ^2.0 or ~2.0 (or something else)

composer.json

@@ -25,7 +25,7 @@
         "symfony/twig-bundle": "~2.3|~3.0",
         "symfony/form": "~2.3|~3.0",
         "symfony/console": "~2.3|~3.0",
-        "twig/twig": "^1.14.2",
+        "twig/twig": "^1.14.2|^2.0",
         "mopa/composer-bridge": "~1.3"
     },
     "require-dev": {