Move async execution from celluloid to concurrent-ruby

This removes 8 runtime gem dependencies from Rails:

```
Using hitimes 1.2.3
Using timers 4.1.1
Using celluloid-essentials 0.20.5
Using celluloid-extras 0.20.5
Using celluloid-fsm 0.20.5
Using celluloid-pool 0.20.5
Using celluloid-supervision 0.20.5
Using celluloid 0.17.2
```

1 files changed, 1 insertions, 1 deletions

diff --git a/actioncable/lib/action_cable/connection/base.rb b/actioncable/lib/action_cable/connection/base.rb
index 977856d656..a8cfdf90f3 100644
--- a/actioncable/lib/action_cable/connection/base.rb
+++ b/actioncable/lib/action_cable/connection/base.rb
@@ -103,7 +103,7 @@ module ActionCable
 
       # Invoke a method on the connection asynchronously through the pool of thread workers.
       def send_async(method, *arguments)
-        worker_pool.async.invoke(self, method, *arguments)
+        worker_pool.async_invoke(self, method, *arguments)
       end
 
       # Return a basic hash of statistics for the connection keyed with `identifier`, `started_at`, and `subscriptions`.