commands: Fix broken hugo --renderToMemory

The `--renderToMemory` flag stopped working on `hugo` in 0.32.

Note that this is only useful for benchmark testing, as there is no easy way to actually view the result.

Fixes #4212

commands/hugo.go

@@ -132,6 +132,7 @@ Complete documentation is available at http://gohugo.io/.`,
 			if buildWatch {
 				c.Set("disableLiveReload", true)
 			}
+			c.Set("renderToMemory", renderToMemory)
 			return nil
 		}