Fix php-cs-fixer requirement

Author: rikbruil

composer.json

@@ -26,7 +26,7 @@
   "require-dev": {
     "phpspec/phpspec": "^2.0",
     "henrikbjorn/phpspec-code-coverage": "^2.0",
-    "friendsofphp/php-cs-fixer": "^1.12",
+    "friendsofphp/php-cs-fixer": "v1.12.0",
     "satooshi/php-coveralls": "^1.0"
   },
   "extra": {