Drop PHP < 7.0

Merge pull request #41 from KnpLabs/drop-php-before-7.0

Drop PHP support before 7.0

v2.1

Support invokable (#35)

* Ensure "arguments" parameter is always an array

* Allow invokable in every format

* Refactor ResourceResolverSpec

* Add supports for invokable to ResourceResolver

* Add more examples of invokable usage

* Fix prophecy version

Symfony3 support

Merge pull request #26 from KnpLabs/feature/sf3-update

Support Symfony3 version

v1.4.0

v1.4.0