roll emscripten on the bots

This 1.39.4 is the current "latest", the recommended version.

I'm not quite confident enough to just let this float at "latest",
but I think the way the new directory structure is laid out, we
could, at least until they bump node.

Change-Id: I0aebdea7728bea0d0b8215a49c0d1db56805eb79
Reviewed-by: Mike Klein <>
Commit-Queue: Mike Klein <>
1 file changed