THRIFT-4448: Golang: do something with context.Context. Remove Go1.6 compatibility.
Client: go

This closes #1459
diff --git a/tutorial/go/src/client.go b/tutorial/go/src/client.go
index 25616bf..1d658b9 100644
--- a/tutorial/go/src/client.go
+++ b/tutorial/go/src/client.go
@@ -20,6 +20,7 @@
  */
 
 import (
+	"context"
 	"crypto/tls"
 	"fmt"
 	"tutorial"
@@ -27,6 +28,8 @@
 	"git.apache.org/thrift.git/lib/go/thrift"
 )
 
+var defaultCtx = context.Background()
+
 func handleClient(client *tutorial.CalculatorClient) (err error) {
 	client.Ping(defaultCtx)
 	fmt.Println("ping()")