add wiki_hop
Also the dummy data files are quite big (500KB)
If you could reduce that that would be nice (just look at the files inside and remove unecessary chunks of texts)
in general dummy data are just a few KB and we suggest to not get higher than 50KB

Having light dummy data makes the repo faster to clone
This PR adds the WikiHop dataset from the QAngaroo multi hop reading comprehension datasets

More info:
http://qangaroo.cs.ucl.ac.uk/index.html
