publish a release with ring 0.17

[hoodie]

Hi there! Do you think it would be possible to make a release that includes the ring 0.17 update?

Ring 0.17 is considered a major release so rustc will include both 0.16 and 0.17 in a binary,
but since ring itself contains C-code this causes linker warnings on some platforms.

I've been trying to harmonize my dependencies to all use the same version of ring, and rcgen is the last one to not have a release with 0.17 yet. If you're holding our due to breaking changes, maybe 948c3b5 is a good candidate for a 0.11.4.

Thank you

[cpu]

👍 I think it makes sense to start deciding what needs to land before we cut a 0.12 release.

[cpu]

Let's track this in #199.