panic: repeated read on failed websocket connection

[aripringle]

• Version of phabulous: 3.0.0-beta3
• Version of phabricator: 021c612cb228ad29fb1d4d7f63276cf29bef754a (Sep 24 2018)

We use phabulous very successfully, but it periodically crashes and has to be restarted.

I started running it in a shell so that I could see the output. I ran into the following crash when updating an existing diff:

---

[GIN] 2019/03/14 - 17:01:33 | 200 |  396.807181ms |             ::1 |  POST     /v1/feed/receive
panic: repeated read on failed websocket connection

goroutine 37 [running]:
github.com/etcinit/phabulous/vendor/github.com/gorilla/websocket.(*Conn).NextReader(0xc42042db80, 0xc420213558, 0x0, 0x0, 0xc420360ec0, 0xc420360ec0)
        C:/Users/Martin/Documents/go/src/github.com/etcinit/phabulous/vendor/github.com/gorilla/websocket/conn.go:958 +0x3d9
github.com/etcinit/phabulous/vendor/github.com/gorilla/websocket.(*Conn).ReadJSON(0xc42042db80, 0xad2ec0, 0xc4204084c0, 0xf2b760, 0xf61110)
        C:/Users/Martin/Documents/go/src/github.com/etcinit/phabulous/vendor/github.com/gorilla/websocket/json.go:45 +0x2f
github.com/etcinit/phabulous/vendor/github.com/nlopes/slack.(*RTM).receiveIncomingEvent(0xc4201ccdc0)
        C:/Users/Martin/Documents/go/src/github.com/etcinit/phabulous/vendor/github.com/nlopes/slack/websocket_managed_conn.go:288 +0xaa
github.com/etcinit/phabulous/vendor/github.com/nlopes/slack.(*RTM).handleIncomingEvents(0xc4201ccdc0, 0xc4201f8000)
        C:/Users/Martin/Documents/go/src/github.com/etcinit/phabulous/vendor/github.com/nlopes/slack/websocket_managed_conn.go:223 +0x2d
created by github.com/etcinit/phabulous/vendor/github.com/nlopes/slack.(*RTM).ManageConnection
        C:/Users/Martin/Documents/go/src/github.com/etcinit/phabulous/vendor/github.com/nlopes/slack/websocket_managed_conn.go:54 +0x265