Bump nodejs 8.x and npm 5.x

Bump nodejs 8.x and npm 5.x

Default nodejs & npm are very old (nodejs 4.x and npm 3.x) and don't
allow to build xds dashboard. Note that one reason to bump to a
recent npm version (at least npm ^5.0.0) is the support of
package-lock.json that is very useful to lock dependencies of nodejs
packages in a project.
(for more info see https://docs.npmjs.com/files/package-lock.json)

Change-Id: I639b97ee12e9d11f47a09bf5443fb2470fbf485a
Signed-off-by: Sebastien Douheret <sebastien.douheret@iot.bzh>