Fix the dep on cenkalti

vendor/github.com/cenkalti/backoff/context_test.go

@@ -0,0 +1,26 @@
+package backoff
+
+import (
+	"testing"
+	"time"
+
+	"golang.org/x/net/context"
+)
+
+func TestContext(t *testing.T) {
+	b := NewConstantBackOff(time.Millisecond)
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	cb := WithContext(b, ctx)
+
+	if cb.Context() != ctx {
+		t.Error("invalid context")
+	}
+
+	cancel()
+
+	if cb.NextBackOff() != Stop {
+		t.Error("invalid next back off")
+	}
+}