fix link

Author: lucasmcdonald3

README.rst

@@ -259,7 +259,7 @@ For more information, see the note on thread safety in that project's README (TO
 .. _KMS key identifier: https://docs.aws.amazon.com/kms/latest/developerguide/concepts.html#key-id
 .. _boto3 SDK: https://boto3.readthedocs.io/en/latest/
 .. _standard means by which boto3 locates credentials: https://boto3.readthedocs.io/en/latest/guide/configuration.html
-.. _final message: https://docs.aws.amazon.com/encryption-sdk/latest/developer-guide/message-format.html
+.. _encrypted message: https://docs.aws.amazon.com/encryption-sdk/latest/developer-guide/message-format.html
 .. _encryption context: https://docs.aws.amazon.com/kms/latest/developerguide/concepts.html#encrypt_context
 .. _Security issue notifications: ./CONTRIBUTING.md#security-issue-notifications
 .. _Support Policy: ./SUPPORT_POLICY.rst