chore: cut release 1.2.1

[digitalcora]

Thought it would be nice to get this out, both to unblock ca_store upgrades and to align with the updated README, which now says to add ca_store with a constraint of ~> 1.0 (if you did this with the current published version, there would be a conflict).

@paulswartz if you approve, do you want to handle the publishing to Hex? I haven't done that before and I assume you're already set up for it.

[github-actions]

Coverage of commit c0fe7aa

Summary coverage rate:
  lines......: 100.0% (104 of 104 lines)
  functions..: 92.0% (23 of 25 functions)
  branches...: no data found

Files changed coverage rate: n/a

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