add https option to serve and browsersync config

[Gilles Haiat]

in constants.js

serve: {
host: 'localhost', //'0.0.0.0',
port: 5000,
open: true,
https:true,

in serve.js

host: constants.serve.host,
port: constants.serve.port,
https: constants.serve.https,

ideally, we should add an option to browsersync to switch beetween https and http