Update Javascript version for TripService

[udebella]

Scope of the changes :

• Updated dependencies to be up-to-date with last versions.
• Added NVM (node version manager) to specify node version to use when working on the kata
• Updated code coverage tool to generate coverage report each time we run the test in /coverage folder
• With the last version of node, introduced es6 modules inside the project
• Used Chai as assertion library which is more user friendly than the one bundled in Nodejs.
• Lastly, fixed the user class that was not properly implemented (it is correctly implemented in other languages of this kata)