Update README link to access key (#2661)

README.md

@@ -174,7 +174,7 @@ We work hard to provide a high-quality and useful SDK for our AWS services, and
 [docs-guide-v2]: http://docs.aws.amazon.com/aws-sdk-php/v2/guide/index.html
 [docs-contribution]: https://github.com/aws/aws-sdk-php/blob/master/CONTRIBUTING.md
 [docs-migration]: https://docs.aws.amazon.com/sdk-for-php/v3/developer-guide/getting-started_migration.html
-[docs-signup]: http://aws.amazon.com/developers/access-keys/
+[docs-signup]: https://aws.amazon.com/premiumsupport/knowledge-center/create-access-key/
 [docs-requirements]: https://docs.aws.amazon.com/sdk-for-php/v3/developer-guide/getting-started_requirements.html
 [docs-installation]: https://docs.aws.amazon.com/sdk-for-php/v3/developer-guide/getting-started_installation.html
 [docs-quickstart]: https://docs.aws.amazon.com/sdk-for-php/v3/developer-guide/welcome.html#getting-started