Update node packages to np2nix 5.5.0

Signed-off-by: Shea Levy <shea@shealevy.com>
Revert "Hide nodePackages from nix-env"

Now node packages that aren't just programs have a node- prefix in their
names.

This reverts commit 2f11bc495b50c36c1984f334df6867c1b9200a91.

Signed-off-by: Shea Levy <shea@shealevy.com>