fix(karma): exclude demo files

I am working on #1884 and well, seems to be doable, but karma also adds the demo files and it start complaining if I change the functions to modules. Since we are not doing anything karma-related with the demos, the first step would be excluding them.

With this done, I could work on improving the demos.

I think that the globbing is good enough (I tested it, it seems to work no problem).