Random crash switching connections

Occasionally, slick will crash when switching connections:

```
0xf9)
/usr/local/Cellar/go/1.8.3/libexec/src/crypto/tls/conn.go:488 +0x98
crypto/tls.(*Conn).readRecord(0xc420736000,
0x144a617, 0xc420736120, 0x50)
/usr/local/Cellar/go/1.8.3/libexec/src/crypto/tls/conn.go:590 +0xc4
crypto/tls.(*Conn).R
ead(0xc420736000, 0xc420739000, 0x1000, 0x1000, 0x0, 0x0, 0x0)
/usr/local/Cellar/go/1.8.3/libexec/src/crypto/tls/conn.
go:1134 +0x11d
bufio.(*Reader).fill(0xc4207441e0)
/usr/local/Cellar/go/1.8.3/libexec/src/bufio/bufio.go:97 +0x117

bufio.(*Reader).ReadByte(0xc4207441e0, 0xc42001a9b0, 0x1011b7c, 0xc4206ab5f8)
/usr/local/Cellar/go/1.8.3/libexec/src/
bufio/bufio.go:239 +0x5b
golang.org/x/net/websocket.hybiFrameReaderFactory.NewFrameReader(0xc4207441e0, 0x0, 0x0, 0xc420
010110, 0x1)
/Users/ryan/w/go/src/golang.org/x/net/websocket/hybi.go:123 +0x5d
golang.org/x/net/websocket.(*Conn).Rea
d(0xc42049cf30, 0xc4206c5200, 0x200, 0x200, 0x0, 0x15d8cc0, 0xc420010110)
/Users/ryan/w/go/src/golang.org/x/net/w
ebsocket/websocket.go:197 +0x1bc
github.com/1egoman/slick/gateway/slack.(*SlackConnection).Connect.func1(0xc4204d0bb0, 0
xc4206d2580, 0x1437158, 0x11, 0xc4206d9e00)
/Users/ryan/w/go/src/github.com/1egoman/slick/gateway/slack/connect.go:
53 +0xaf
created by github.com/1egoman/slick/gateway/slack.(*SlackConnection).Connect
/Users/ryan/w/go/src/github.com
/1egoman/slick/gateway/slack/connect.go:101 +0x52c

goroutine 52 [chan receive]:
github.com/1egoman/slick/gateway/slack.(*
SlackConnection).Connect.func2(0xc4206d2580, 0x1437158, 0x11, 0xc4206d9e60)
/Users/ryan/w/go/src/github.com/1egoman
/slick/gateway/slack/connect.go:111 +0xbc
created by github.com/1egoman/slick/gateway/slack.(*SlackConnection).Connect
/
Users/ryan/w/go/src/github.com/1egoman/slick/gateway/slack/connect.go:154 +0x56f

goroutine 53 [sleep]:
time.Sleep(0x6fc23
ac00)
/usr/local/Cellar/go/1.8.3/libexec/src/runtime/time.go:59 +0xf9
github.com/1egoman/slick/gateway/slack.(*SlackCo
nnection).Connect.func3(0xc4206d2580, 0xc4206d9e60)
/Users/ryan/w/go/src/github.com/1egoman/slick/gateway/slack/con
nect.go:161 +0x4c
created by github.com/1egoman/slick/gateway/slack.(*SlackConnection).Connect
/Users/ryan/w/go/src/gi
thub.com/1egoman/slick/gateway/slack/connect.go:174 +0x59d
```