Removes dev-master to avoid problems.

Identified in [Travis build](https://travis-ci.org/LearningLocker/learninglocker/builds/35340186). This pull request restricts the version of [laravel/framework](https://github.com/laravel/framework/compare/v4.2.8...v4.2.9) for now until the [issue in jenssegers/laravel-mongodb](https://github.com/jenssegers/laravel-mongodb/issues/321) is resolved.