Fix test for gzip changes in go1.8

Update dev at the same time.

dev.yml

@@ -1,7 +1,8 @@
 name: sarama
 
 up:
-  - go: 1.7.3
+  - go:
+      version: '1.8'
 
 commands:
   test:

message_test.go

@@ -1,6 +1,7 @@
 package sarama
 
 import (
+	"runtime"
 	"testing"
 	"time"
 )
@@ -24,6 +25,17 @@ var (
 		0x08,
 		0, 0, 9, 110, 136, 0, 255, 1, 0, 0, 255, 255, 0, 0, 0, 0, 0, 0, 0, 0}
 
+	emptyGzipMessage18 = []byte{
+		132, 99, 80, 148, //CRC
+		0x00,                   // magic version byte
+		0x01,                   // attribute flags
+		0xFF, 0xFF, 0xFF, 0xFF, // key
+		// value
+		0x00, 0x00, 0x00, 0x17,
+		0x1f, 0x8b,
+		0x08,
+		0, 0, 0, 0, 0, 0, 255, 1, 0, 0, 255, 255, 0, 0, 0, 0, 0, 0, 0, 0}
+
 	emptyLZ4Message = []byte{
 		132, 219, 238, 101, // CRC
 		0x01,                          // version byte
@@ -79,7 +91,11 @@ func TestMessageEncoding(t *testing.T) {
 
 	message.Value = []byte{}
 	message.Codec = CompressionGZIP
-	testEncodable(t, "empty gzip", &message, emptyGzipMessage)
+	if runtime.Version() == "go1.8" {
+		testEncodable(t, "empty gzip", &message, emptyGzipMessage18)
+	} else {
+		testEncodable(t, "empty gzip", &message, emptyGzipMessage)
+	}
 
 	message.Value = []byte{}
 	message.Codec = CompressionLZ4