update scrapelib to 0.10.0, remove follow_robots kwarg

[scrapelib](https://github.com/sunlightlabs/scrapelib) updated to `0.10`, and removed the `follow_robots` parameter and default behavior.

Unfortunately, removing the follow_robots keyword and *not* updating to `0.10` has the effect of enforcing robots.txt checking.

So after merging, **anyone with this deployed needs to re-run `pip install -r requirements.txt`**. This will fix the 
[currently broken build in Travis CI](https://travis-ci.org/unitedstates/congress-legislators/builds/31331752) as well.

I'll leave it to a project owner to merge.