Implement Travis Continuous Integration

[LaimeJesus]

It would be nice to set a Continuous Integration tool so we can be sure that new changes does not break anything when they are merged.
A new .travis.yml file should be added in the root folder. At the moment, we just want to be sure that the app build works, so It is only needed to add the configuration to build our app for the web environment.
After that, we should add a new badge into the README.md which will allow us to see the current status of our CI.

References:

• https://docs.travis-ci.com/user/tutorial/#to-get-started-with-travis-ci
• https://docs.travis-ci.com/user/status-images/