First attempt at getting it to work with elixir 1.0
Elixir 1.0 update

Fixed up syntax to meet 1.0 requirements. Added Watcher.Supervisor.add!
which raises an exception if there was an error in the process of adding
a watcher_supervisor
Merge pull request #1 from hderms/elixir_1.0

Elixir 1.0 version compatibility