skein: bump threefish to v0.6.0-rc.0 (#769)

Author: tarcieri

Cargo.lock

@@ -14,7 +14,7 @@ categories = ["cryptography", "no-std"]
 
 [dependencies]
 digest = "0.11.0-rc.5"
-threefish = { version = "0.5.2", default-features = false }
+threefish = { version = "0.6.0-rc.0", default-features = false }
 
 [dev-dependencies]
 digest = { version = "0.11.0-rc.5", features = ["dev"] }