Update *ring* to 0.17 and untrusted to 0.9.

Intentionally use "0.17" as the version spec instead of the latest
version "0.17.7" to help projects depending on rust-tuf who want to
go through a two step ring 0.16.20 -> 0.17.0 -> 0.17.7 update
process.

Since *ring* 0.17 uses untrusted 0.9 currently, update rust-tuf to
use that same version.

Author: briansmith

tuf/Cargo.toml

@@ -26,13 +26,13 @@ hyper = { version = "0.14.15", default-features = false, features = [ "stream",
 itoa = "1.0"
 log = "0.4"
 percent-encoding = "2.1"
-ring = { version = "0.16" }
+ring = { version = "0.17" }
 serde = "1"
 serde_derive = "1"
 serde_json = "1"
 tempfile = "3"
 thiserror = "1.0"
-untrusted = "0.7"
+untrusted = "0.9"
 url = "2"
 
 [dev-dependencies]