Restart worker fails to restart and dies on closed stream

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W, [2018-09-18T04:37:55.107838 #220]  WARN -- : DOWN: name=Team, id=T..., 2 retries left
W, [2018-09-18T04:38:55.238204 #220]  WARN -- : DOWN: name=Team, id=T..., 1 retry left
W, [2018-09-18T04:39:55.361735 #220]  WARN -- : DOWN: name=Team, id=T..., 0 retries left
W, [2018-09-18T04:39:55.361934 #220]  WARN -- : RESTART: name=Team, id=T...
W, [2018-09-18T04:39:55.362279 #220]  WARN -- : Error restarting team 5996f4422a947200b1c10399: closed stream.
D, [2018-09-18T04:39:55.362360 #220] DEBUG -- : PING: name=Team, id=T..., done.

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Still a problem, that didn't fix it :(

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W, [2018-09-25T23:52:02.822982 #213]  WARN -- : Error closing driver for 568e992e012d800003000004: closed stream.
W, [2018-09-25T23:52:02.823149 #213]  WARN -- : Error restarting team 568e992e012d800003000004: closed stream.

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19:58:53 console.1 | E, [2018-09-25T19:58:53.905879 #43147] ERROR -- : closed stream (IOError)
19:58:53 console.1 | /Users/dblock/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/openssl/buffering.rb:388:in `syswrite_nonblock'
19:58:53 console.1 | /Users/dblock/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/openssl/buffering.rb:388:in `write_nonblock'
19:58:53 console.1 | /Users/dblock/.rvm/gems/ruby-2.5.1/gems/async-io-1.15.5/lib/async/io/generic.rb:128:in `async_send'
19:58:53 console.1 | /Users/dblock/.rvm/gems/ruby-2.5.1/gems/async-io-1.15.5/lib/async/io/generic.rb:47:in `block in wrap_blocking_method'
19:58:53 console.1 | /Users/dblock/.rvm/gems/ruby-2.5.1/gems/async-websocket-0.6.1/lib/async/websocket/connection.rb:93:in `write'
19:58:53 console.1 | /Users/dblock/.rvm/gems/ruby-2.5.1/gems/websocket-driver-0.7.0/lib/websocket/driver/hybi.rb:228:in `send_frame'
19:58:53 console.1 | /Users/dblock/.rvm/gems/ruby-2.5.1/gems/websocket-driver-0.7.0/lib/websocket/driver/hybi.rb:191:in `frame'
19:58:53 console.1 | /Users/dblock/.rvm/gems/ruby-2.5.1/gems/websocket-driver-0.7.0/lib/websocket/driver/hybi.rb:154:in `close'
19:58:53 console.1 | /Users/dblock/.rvm/gems/ruby-2.5.1/gems/async-websocket-0.6.1/lib/async/websocket/connection.rb:97:in `close'

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@ioquatix could use a bit of help here, I think I am not closing this thing correctly in all cases:

1. Async::IO::SSLSocket#close
2. Slack::RealTime::Concurrency::Async::Socket#close
3. Slack::RealTime::Concurrency::Async::Socket#emit(close event)

This works most of the time, but sometimes ends up with IOError in 2). Looking at the order it makes sense that sending a frame over a closed SSL socket shouldn't work. But then why does it work most of the time? And what's the correct order of force-closing this connection?

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In #93 the ping worker has been removed in favor of an implementation in slack-ruby-client.