remove :crypto.hmac/3 from auth scram

Author: aenglisc

lib/mongo/auth/scram.ex

@@ -75,16 +75,16 @@ defmodule Mongo.Auth.SCRAM do
   end
 
   defp generate_proof(salted_password, auth_message, digest) do
-    client_key   = :crypto.hmac(digest, salted_password, "Client Key")
+    client_key   = :crypto.mac(:hmac, digest, salted_password, "Client Key")
     stored_key   = :crypto.hash(digest, client_key)
-    signature    = :crypto.hmac(digest, stored_key, auth_message)
+    signature    = :crypto.mac(:hmac, digest, stored_key, auth_message)
     client_proof = xor_keys(client_key, signature, "")
     "p=#{Base.encode64(client_proof)}"
   end
 
   defp generate_signature(salted_password, auth_message, digest) do
-    server_key = :crypto.hmac(digest, salted_password, "Server Key")
-    :crypto.hmac(digest, server_key, auth_message)
+    server_key = :crypto.mac(:hmac, digest, salted_password, "Server Key")
+    :crypto.mac(:hmac, digest, server_key, auth_message)
   end
 
   defp xor_keys("", "", result), do: result