[display real data] show a loader while fetching results

[giogonzo]

<- #22

requirements

• show a loader while the http call to github is ongoing

specs

• use LoadingSpinner from: https://github.com/buildo/react-components/tree/master/src/loading-spinner
• import css called style.scss. Note: need to be refactored
• Use the state and check if value are fetched correctly or not inside of a returned Promise