0.16.8: Depend on spin-rs ^0.5.2.

spin-rs 0.5.2 fixes a bug in `rw_lock`. That bug doesn't seem to affect *ring* based
on the bug report and the fix PR, since *ring* uses only `spin::Once` and the fix
for the bug doesn't touch `spin::Once` at all. (I manually verified `spin::Once`
doesn't depend on `spin::rw_lock` at all.) Still, upgrade so that people don't get
scared and to avoid various inconveniences.

Author: briansmith

Cargo.toml

@@ -10,7 +10,7 @@ license-file = "LICENSE"
 name = "ring"
 readme = "doc/link-to-readme.md"
 repository = "https://github.com/briansmith/ring"
-version = "0.16.7"
+version = "0.16.8"
 
 # Prevent multiple versions of *ring* from being linked into the same program.
 links = "ring-asm"
@@ -304,7 +304,7 @@ name = "ring"
 untrusted = { version = "0.7.0" }
 
 [target.'cfg(all(any(target_arch = "aarch64", target_arch = "arm", target_arch = "x86", target_arch = "x86_64"), not(target_os = "ios")))'.dependencies]
-spin = { version = "0.5.0", default-features = false }
+spin = { version = "0.5.2", default-features = false }
 
 
 [target.'cfg(any(target_os = "android", target_os = "linux"))'.dependencies]