Reactor::Eventable doesn't fire all registered procs of an event when a proc unregisters itself

```ruby
proc1 = proc do
  puts 'proc 1'
  off(:foo, &proc1)
end
proc2 = proc do
  puts 'proc 2'
end
on(:foo, &proc1)
on(:foo, &proc2)
trigger(:foo)
````
`proc2`is never called:
```ruby
=> "proc 1"
```