node & npm builder uses too old versions

[abom]

Current node and npm versions installed by the builder are too old, some new packages cannot be build (newer es features...etc).

for example, building threefold.io website

git clone git@github.com:threefoldfoundation/www_threefold.io_new.git
npm install
npm run build

> svelte-app@1.0.0 build /sandbox/code/github/threefoldfoundation/www_threefold.io_new
> rollup -c

[!] SyntaxError: Unexpected token function
/sandbox/code/github/threefoldfoundation/www_threefold.io_new/node_modules/svelte/compiler.js:23956
        async function replace_async(str, re, func) {
              ^^^^^^^^
SyntaxError: Unexpected token function
    at Object.exports.runInThisContext (vm.js:76:16)
    at Module._compile (module.js:542:28)
    at Module._extensions..js (module.js:579:10)
    at Object.require.extensions..js (/sandbox/code/github/threefoldfoundation/www_threefold.io_new/node_modules/rollup/dist/bin/rollup:841:17)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/sandbox/code/github/threefoldfoundation/www_threefold.io_new/node_modules/rollup-plugin-svelte/index.js:11:4)

Current versions:

$ node -v
v6.9.5
$ npm -v
3.10.10

We need at least current lts versions

$ node -v
v10.16.3
$ npm --version
6.9.0

and of course, we need to remove this kind of checks too

        rc, out, err = j.sal.process.execute("npm -v")
        if out.replace("\n", "") != "3.10.10":
            raise j.exceptions.Base("npm version error")

[hossnys]

verified on development 65567fb :

3BOTDEVEL:3bot:~: npm -v
6.9.0
3BOTDEVEL:3bot:~: node -v
v10.16.3