Move build instructions to the before_script section in .travis.yml
Move build instructions to the before_script section in .travis.yml

It makes no sense to let Travis launch the unit tests if the program
failed to compile.

https://docs.travis-ci.com/user/customizing-the-build#Breaking-the-Build
asrob-uc3m/robotDevastation,asrob-uc3m/robotDevastation