Enhancement: Require more recent phpspec/phpspec

[localheinz]

This PR

• requires a more recent phpspec/phpspec
• flattens the directory structure

💁 Before this change, whenever you do the describe and run thing, the actual class would be created in src/League/Event, rather than in src/.

Before

$ bin/phpspec describe League\\\Event\\\LazyListener
Specification for League\Event\LazyListener created in /Users/am/Sites/thephpleague/event/spec/League/Event/LazyListenerSpec.php. 

and then

$ bin/phpspec run spec/League/Event/LazyListenerSpec.php

...

Class League\Event\LazyListener created in /Users/am/Sites/thephpleague/event/src/League/Event/LazyListener.php.

Before

$ bin/phpspec describe League\\\Event\\\LazyListener
Specification for League\Event\LazyListener created in /Users/am/Sites/thephpleague/event/spec/LazyListenerSpec.php. 

and then

$ bin/phpspec run spec/LazyListenerSpec.php
...

Class League\Event\LazyListener created in /Users/am/Sites/thephpleague/event/src/LazyListener.php.