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.
force monolog to >=1.0,<1.3-dev
Merge pull request #25 from drmonty/patch-1

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