Update .travis.yml
Update .travis.yml

```catkin_make_isolated``` enables rostests to import Python code
ZdenekM/artable,Kapim/artable,ZdenekM/artable,ZdenekM/artable,robofit/artable,Kapim/artable,ZdenekM/ar-table-itable,robofit/ar-table-itable,robofit/artable,Kapim/ar-table-itable,robofit/ar-table-itable,Kapim/artable,ZdenekM/ar-table-itable,Kapim/ar-table-itable,robofit/artable,ZdenekM/ar-table-itable