See sebastianbergmann@0edb5c6#commitcomment-12482120

Author: sebastianbergmann

composer.json

@@ -25,7 +25,7 @@
         "phpunit/php-file-iterator": "~1.3",
         "phpunit/php-token-stream": "~1.3",
         "phpunit/php-text-template": "~1.2",
-        "sebastian/environment": "~1.3.1",
+        "sebastian/environment": "^1.3.1",
         "sebastian/version": "~1.0"
     },
     "require-dev": {