Uses ring 0.13 directly

Author: zonyitoo

Cargo.toml

@@ -50,7 +50,7 @@ lazy_static = "1.0"
 serde_json = "1.0"
 base64 = "0.9"
 bytes = "0.4"
-ring = "0.13.0-alpha"
+ring = "0.13"
 md-5 = "0.7"
 digest = "0.7"
 typenum = "1.10"