Remove PHP extension dependencies from composer.json.

These restrictions make it impossible to integrate Boris as an optional part of a larger framework, such as Laravel.
Move PHP-ext from require to suggest section in composer.json


Related with #53
Merge pull request #1 from rogeriopradoj/patch-1

Move PHP-ext from require to suggest section in composer.json
Merge pull request #53 from taylorotwell/master

Remove PHP extension dependencies from composer.json.