Upgrade md5

Author: sfackler

postgres-protocol/Cargo.toml

@@ -15,7 +15,7 @@ bytes = "0.4"
 fallible-iterator = "0.1"
 generic-array = "0.12"
 hmac = "0.7"
-md5 = "0.5"
+md5 = "0.6"
 memchr = "2.0"
 rand = "0.6"
 sha2 = "0.8"