Update metadata docs URL (#80)

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Description of changes:

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Author: arjunrn

metadata.yaml

@@ -2,7 +2,7 @@ service:
   full_name: "Amazon DynamoDB"
   short_name: "DynamoDB"
   link: "https://aws.amazon.com/dynamodb/"
-  documentation: "https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/index.html"
+  documentation: "https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Introduction.html"
 api_versions:
   - api_version: v1alpha1
     status: available