update meta-data docs link (#223)

Issue #, if available:

Description of changes:
Link to docs has been updated, original link now redirects to this new updated one.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: ryansteakley

metadata.yaml

@@ -2,7 +2,7 @@ service:
   full_name: "Amazon SageMaker"
   short_name: "SageMaker"
   link: "https://aws.amazon.com/sagemaker/"
-  documentation: "https://docs.aws.amazon.com/sagemaker/latest/dg/what-is.html"
+  documentation: "https://docs.aws.amazon.com/sagemaker/latest/dg/whatis.html"
 api_versions:
   - api_version: v1alpha1
     status: available