Update Porter to `nucypher` `rc.8`

[derekpierre]

Type of PR:

• [ ] Bugfix
• [ ] Feature
• [ ] Documentation
• [X] Other

Required reviews:

• [ ] 1
• [X] 2
• [ ] 3

What this does: Updates Porter to depend on nucypher `rc.8

Issues fixed/closed:

• Fixes #...

Why it's needed:

Explain how this PR fits in the greater context of the NuCypher Network. E.g., if this PR addresses a nucypher/productdev issue, let reviewers know!

Notes for reviewers:

What should reviewers focus on? Is there a particular commit/function/section of your PR that requires more attention from reviewers?