renamed type hinting to correctly reference DomainEventStreamInterface

renamed type hinting to correctly reference DomainEventStreamInterface
Typehint against DomainEventStreamInterface instead of concrete impl.
Merge pull request #70 from GazEdge/refactor

renamed type hinting to correctly reference DomainEventStreamInterface
Merge pull request #71 from rjkip/maintenance/event-stream-typehint

Typehint against DomainEventStreamInterface instead of concrete implementation
Added PHP 5.4, 5.6 to build matrix