fixed Composer constraints

Author: fabpot

composer.json

@@ -20,7 +20,7 @@
         "symfony/polyfill-php55": "~1.0"
     },
     "require-dev": {
-        "symfony/yaml": "~2.0,>=2.0.5|~3.0.0",
+        "symfony/yaml": "^2.0.5|~3.0.0",
         "symfony/config": "~2.2|~3.0.0",
         "symfony/property-access": "~2.3|~3.0.0",
         "doctrine/annotations": "~1.0",