[MRG+1] MAINT skip tests that require large datadownload under travis

The text tutorial requires the 20 newsgroups data that gets downloaded over and over by stateless travis workers wasting a significant amount of bandwith.

Furthermore this should reduce memory pressure that caused some either failures when calling `os.fork()` on a large Python process on loaded travis workers.
I wasn't aware of these `*_fixture.py` files. The other ones in the repo have an introductory docstring. I think that would be helpful here