add a git clone of gemoc-studio repository in travis.yml
add a git clone of gemoc-studio repository in travis.yml

This should enables tests using its contents
SiriusLab/SiriusAnimator,SiriusLab/ModelDebugging,SiriusLab/SiriusAnimator,SiriusLab/ModelDebugging,SiriusLab/ModelDebugging,SiriusLab/SiriusAnimator