prevent using monolog 1.3.x-dev before PSR-3

Before symfony isn't updated to PSR-3, monolog 1.3.x-dev will lead to fatal error.
Force monolog to latest stable.

Author: mrohnstock

composer.json

@@ -20,7 +20,7 @@
         "symfony/monolog-bridge": ">=2.1.0,<2.3-dev",
         "symfony/dependency-injection": ">=2.1.0,<2.3-dev",
         "symfony/config": ">=2.1.0,<2.3-dev",
-        "monolog/monolog": "1.*"
+        "monolog/monolog": "<=1.2.1"
     },
     "require-dev": {
         "symfony/yaml": ">=2.1.0,<2.3-dev",