PHP7SupportforLaravel4.2

This pull request aims to bring PHP7 support for Laravel 4.2 packages, which officially support PHP7.

All credits goes to from his comment here: https://github.com/alcaeus/mongo-php-adapter/issues/107#issuecomment-219393254

Also, another discussion regarding this issue here: https://github.com/LearningLocker/learninglocker/issues/893

If this specific version is selected as requirement, this may break compatibility with PHP versions lower than 5.6, and since there hasn't been an update to 2.0 branch for a while, I believe, if this would be accepted, a simple note would suffice for users.

Thanks in advance,

该提问来源于开源项目：jenssegers/laravel-mongodb