Loosen unidiff pinning

[jonashaag]

Right now there is a pin to 0.7.4. Is this on purpose or can be make it less strict, say >=0.7.4,<0.8?

[danvk]

Yes, it could be made less strict. ^0.7.4 is fine. I'd be happy to merge a PR for this.

I don't think there's any particular reason for this precise pin. It goes back to when I was using setup.py years ago: https://github.com/danvk/webdiff/pull/150/files#diff-60f61ab7a8d1910d86d9fda2261620314edcae5894d5aaa236b821c7256badd7R29