mozjs38 new package in zesty

[Jeremy Bicha]

Hi,

Archive Admins, please review mozjs38 for acceptance into zesty.
https://pad.lv/1662094

I apologize for not uploading this sooner but I was waiting for the
GNOME port to mozjs38 to be successful so that we wouldn't need to
have mozjs31 in Ubuntu too.

These universe package updates need mozjs38:
gjs 1.47.90
gnome-shell 3.23.90
mutter 3.23.90

Thanks,
Jeremy