Merge pull request #3974 from creack/3967-add_content_type-fix

Add json content type to /containers/json api endpoint
Upstream-commit: 22aeae34c1d257956e6201697e30dd64028a1182
Component: engine

components/engine/api/api.go

@@ -320,6 +320,7 @@ func getContainersJSON(eng *engine.Engine, version float64, w http.ResponseWrite
 	job.Setenv("limit", r.Form.Get("limit"))
 
 	if version >= 1.5 {
+		w.Header().Set("Content-Type", "application/json")
 		job.Stdout.Add(w)
 	} else if outs, err = job.Stdout.AddTable(); err != nil {
 		return err