api: Remove omitempty tag on Parallelism

It doesn't make sense to use omitempty here. 0 is a meaningful value and
it's different from the default. If someone sets Parallelism to 0, we
want to show that Parallelism is 0, not hide the field.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
(cherry picked from commit d8b8b129948ef8586f5b2f576533952419e302f2)
Signed-off-by: Victor Vieux <victorvieux@gmail.com>

api/types/swarm/service.go

@@ -74,7 +74,7 @@ const (
 type UpdateConfig struct {
 	// Maximum number of tasks to be updated in one iteration.
 	// 0 means unlimited parallelism.
-	Parallelism uint64 `json:",omitempty"`
+	Parallelism uint64
 
 	// Amount of time between updates.
 	Delay time.Duration `json:",omitempty"`