Bug-bounty Updates

[jalextowle]

• [x] Disable Immunifi for Council (cc. @jrhea, @CPSTL, @jalextowle)
• [x] Consider switching to Cantina
• [ ] Review SOW from Cantina (cc. @jrhea, @smaroo, @CPSTL, @jalextowle)

[jalextowle]

We made a decision. We're going to lock it in, and we'll close this issue once it's signed.