CSHARP-1331: changed SHA256 algorithm to one that is FIPS compliant.

Author: craiggwilson

src/MongoDB.Driver/PasswordEvidence.cs

@@ -127,7 +127,7 @@ private static SecureString CreateSecureString(string str)
         /// </summary>
         private static string GenerateDigest(SecureString secureString)
         {
-            using (var sha256 = new SHA256Managed())
+            using (var sha256 = new SHA256CryptoServiceProvider())
             {
                 TransformFinalBlock(sha256, secureString);
                 return BsonUtils.ToHexString(sha256.Hash);