Improve the example InvitesTest

The InvitesTest example used a hardcoded aggregate id of 1 in each
tests, which also corresponds to the default id in the
Broadway\CommandHandling\Testing\Scenario, making it not quite so
obvious as to how to work with the real aggregate id when doing
scenario testing.

This commit changes the InvitesTest to generate a new UUID in each
test and passes it through to Scenario::withAggregateId() to give
a better (more real-world) example of the proper way to use the
Scenario class
Merge pull request #66 from mbadolato/improve_example_invites_test

Improve the example InvitesTest
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
Merge pull request #63 from wjzijderveld/update-travis

Added PHP 5.4, 5.6 and HHVM to build matrix