Update gonx to support variables with uppercase letters

[ngauthier]

honeycombio/gonx@dc1c4fe allows parsing fields with uppercase characters. This will allow honeytail to parse nginx fields like traceId which will allow traces from nginx logs.

Please bump the dependency on gonx to at least dc1c4fe6e0cc63c38a537b78f9ddaa60e168b957

[ngauthier]

Here is an example failing test (I modified the first test in the nginx_test.go file):

func TestProcessLines(t *testing.T) {
	t1, _ := time.ParseInLocation(commonLogFormatTimeLayout, "08/Oct/2015:00:26:26 -0000", time.UTC)
	preReg := &parsers.ExtRegexp{regexp.MustCompile("^.*:..:.. (?P<pre_hostname>[a-zA-Z-.]+): ")}
	tlm := []testLineMaps{
		{
			line:        "Nov 05 10:23:45 myhost: https - 10.252.4.24 - - [08/Oct/2015:00:26:26 +0000] 200 174 0.099 a873d74c-4588-4a25-b3ed-77d23fe6275a 17d22fa7-796e-85f6-3d58-2d6e693da860",
			trimmedLine: "https - 10.252.4.24 - - [08/Oct/2015:00:26:26 +0000] 200 174 0.099 a873d74c-4588-4a25-b3ed-77d23fe6275a 17d22fa7-796e-85f6-3d58-2d6e693da860",
			ev: event.Event{
				Timestamp: t1,
				Data: map[string]interface{}{
					"pre_hostname":           "myhost",
					"body_bytes_sent":        int64(174),
					"http_x_forwarded_proto": "https",
					"remote_addr":            "10.252.4.24",
					"request_time":           0.099,
					"status":                 int64(200),
					"traceId":                "a873d74c-4588-4a25-b3ed-77d23fe6275a",
					"id":                     "17d22fa7-796e-85f6-3d58-2d6e693da860",
				},
			},
		},
	}
	p := &Parser{
		conf: Options{
			NumParsers: 5,
		},
		lineParser: &GonxLineParser{
			parser: gonx.NewParser("$http_x_forwarded_proto - $remote_addr - $remote_user [$time_local] $status $body_bytes_sent $request_time $traceId $id"),
		},
	}
	lines := make(chan string)
	send := make(chan event.Event)
	go func() {
		for _, pair := range tlm {
			lines <- pair.line
		}
		close(lines)
	}()
	go p.ProcessLines(lines, send, preReg)
	for _, pair := range tlm {
		resp := <-send
		if !reflect.DeepEqual(resp, pair.ev) {
			t.Fatalf("line resp didn't match up for %s. Expected: %+v, actual: %+v",
				pair.line, pair.ev, resp)
		}
	}
}