Merge pull request #2507 from mistyhacks/fix-storage-driver-link

Fixed broken storage driver link

docs/spec/index.md

@@ -7,6 +7,6 @@ keywords: registry, service, images, repository,  json
 # Docker Registry Reference
 * [HTTP API V2](api.md)
-* [Storage Driver](../storage-drivers/index.md)
+* [Storage Driver](https://docs.docker.com/registry/storage-drivers/)
 * [Token Authentication Specification](auth/token.md)
 * [Token Authentication Implementation](auth/jwt.md)