Update to Swift 8-15

[edjiang]

Blocked on vapor/engine, vapor/json, and SecretSocks. @tannernelson, I'm doing other work this week -- can you ping me when the vapor dependencies are ready? If SecretSocks needs work I can take a look into it.

[edjiang]

Task list right now: I'm checking off ones with active PRs

• [ ] Engine https://github.com/vapor/engine
  • [ ] SHA1 https://github.com/CryptoKitten/SHA1
  • [ ] CryptoEssentials https://github.com/CryptoKitten/CryptoEssentials
  • [x] Socks https://github.com/czechboy0/Socks
  • [x] Core https://github.com/vapor/core
  • [x] Strand https://github.com/ketzusaka/Strand
• [x] SecretSocks https://github.com/czechboy0/SecretSocks
  • [x] Socks https://github.com/czechboy0/Socks
  • [x] TLS https://github.com/qutheory/tls
  • [x] COpenSSL https://github.com/Zewo/COpenSSL@0.6.2>

[edjiang]

@tannernelson btw I think I'm going to use JSONSerialization for the next release (since it seems to be OK on linux now?), so no worries about updating that.

[tanner0101]

vapor/JSON is just a wrapper around Foundation's JSON. Core should be good with version 0.5 and Joannis is working on making our crypto lib 8-18 compatible.