optimisation: pre-allocate some maps

This doesn't make much of a difference, since we don't create many of
these. But it's easy enough to do, and every little helps.

render/container.go

@@ -131,7 +131,7 @@ func (r containerWithImageNameRenderer) Render(rpt report.Report) Nodes {
 	containers := r.Renderer.Render(rpt)
 	images := SelectContainerImage.Render(rpt)
 
-	outputs := report.Nodes{}
+	outputs := make(report.Nodes, len(containers.Nodes))
 	for id, c := range containers.Nodes {
 		outputs[id] = c
 		imageID, ok := c.Latest.Lookup(docker.ImageID)

render/process.go

@@ -42,7 +42,7 @@ func (r processWithContainerNameRenderer) Render(rpt report.Report) Nodes {
 	processes := r.Renderer.Render(rpt)
 	containers := SelectContainer.Render(rpt)
 
-	outputs := report.Nodes{}
+	outputs := make(report.Nodes, len(processes.Nodes))
 	for id, p := range processes.Nodes {
 		outputs[id] = p
 		containerID, timestamp, ok := p.Latest.LookupEntry(docker.ContainerID)