Fixing link to bitcoin service docs

Author: karelbilek

docs/upgrade.md

@@ -73,5 +73,5 @@ rpcpassword=<password>
 **Important**: Once changes have been made you'll also need to add the `reindex=1` option **only for the first startup** to regenerate the indexes. Once this is complete you should be able to remove the `bitcore-node.db` directory with the old indexes.
 
 ### API and Service Changes
-- Many API methods that were a part of the `db` and `address` services are now a part of the `bitcoind` service. Please see [Bitcoin Service Docs](docs/services/bitcoind.md) for more details.
-- The `db` and `address` services are deprecated, most of the functionality still exists. Any services that were extending indexes with the `db` service, will need to manage chain state itself, or build the indexes within `bitcoind`.
+- Many API methods that were a part of the `db` and `address` services are now a part of the `bitcoind` service. Please see [Bitcoin Service Docs](services/bitcoind.md) for more details.
+- The `db` and `address` services are deprecated, most of the functionality still exists. Any services that were extending indexes with the `db` service, will need to manage chain state itself, or build the indexes within `bitcoind`.