Enable Splunk logdriver for windows

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

daemon/logdrivers_windows.go

@@ -5,4 +5,5 @@ import (
 	// therefore they register themselves to the logdriver factory.
 	_ "github.com/docker/docker/daemon/logger/awslogs"
 	_ "github.com/docker/docker/daemon/logger/jsonfilelog"
+	_ "github.com/docker/docker/daemon/logger/splunk"
 )