Bill 6: Make bills link to visual diff on github (PR #244)

Apparently, for reasons I don't remember, I changed the diff links in the fixtures to point to the visual diff in github even though the automation depends on the url being the raw diff. It doesn't actually matter since obviously the fixtures can't be merged, but when someone tried to open the link on the website, they were shown the raw diff, which made no sense.
Diff: +10 -5