Validated travis.yml file

Hooray, your .travis.yml seems to be solid!

It will generate 4 jobs:

compiler="gcc", env="RBDEMO_TRAVIS_BUILD_TYPE=Debug"
compiler="gcc", env="RBDEMO_TRAVIS_BUILD_TYPE=Release"
compiler="clang", env="RBDEMO_TRAVIS_BUILD_TYPE=Debug"
compiler="clang", env="RBDEMO_TRAVIS_BUILD_TYPE=Release"