writePump error from slackarchive

Hi! I'm trying to get SlackArchive running as well, and I ran into a few issues that I was able to solve with the help of the issues mentioned here on github. Especially the elasticsearch one. Thanks for that!

I'm still having 2 issues remaining so I'm logging 2 issues for this, I hope that's ok. This is the first one. I still don't see anything on the web interface:

Now, I think this is to do with the 2 problems I'm seeing. The first one seems to do with the bot interfacing to the slackarchive docker. I see this in the logs:

```
slackarchive-bot_1       | nlopes/slack2019/02/17 20:53:32 websocket_managed_conn.go:307: Incoming Event: {"type": "hello"}
slackarchive_1           | 2019/02/17 20:53:33 writePump error: %!(EXTRA string=write tcp 172.18.0.4:8080->172.18.0.5:50174: write: broken pipe)
slackarchive_1           | 2019/02/17 20:53:33 Connection closed
```

Is this a common problem perhaps? I did set up the network as instructed, and I also made sure the bot token is the same in both yaml files..

Start by reproducing the Docker setup described in the issue and inspect the slackarchive container logs around the writePump error and Connection closed message. Trace the websocket connection associated with websocket_managed_conn.go:307 and compare the bot and slackarchive YAML network and token settings; done means identifying the cause of the broken pipe and confirming the web interface receives archived data.

Written by the indexing model from the issue text.