Add Travis-CI build status badge

[SubhrajyotiSen]

Reviewer: Asana: CC:

Reviewer Checklist:

• [x] Ensure the PR solves the problem
• [x] Review every line of code
• [x] Ensure the PR does no harm by testing the changes thoroughly
• [x] Get help if you're uncomfortable with any of the above!
• [x] Determine if there are any quick wins that improve the implementation

PR DRI Checklist:

• [ ] Get advice or leverage existing code
• [ ] Agree on technical approach with reviewer (if the changes are nuanced)
• [ ] Ensure that there is a testing strategy (and documented non-automated tests)
• [ ] Ensure there is a documented monitoring strategy (if necessary)
• [ ] Consider systems implications (Database connections, Grafana stats, CPU)

[fgei]

thanks @SubhrajyotiSen!