Pin CSV to 1.1.6

[mitsuhiko]

CSV now requires 1.60, trying to see if pinning to 1.1.6 works to retain lower MSRV.

[joshuataylor]

Is there a way to workaround the issue where:

1. Using csv in dependencies, currently version 1.3.0 (doesn't matter, imagine a higher version)
2. Using insta in dev-dependencies
3. To use csv, now I need to also pin to =1.1.6

Not sure if there is a clean/sane way of doing this? In other languages, you can override a transitive dependency version for a library (if you're brave, I guess).

[max-sixty]

That is a bit unfortunate. I'm not familiar with a workaround; I don't think cargo generally allows this when both come from crates.io.

#524 would allow us to unlock the dependency while maintaining MSRV, but it needs a review...