Fix second link to bitcoin service docs

Author: Braydon Fuller

docs/upgrade.md

@@ -18,7 +18,7 @@ To start reindexing add `reindex=1` during the **first startup only**.
 ### Configuration Options
 
 - The `bitcoin.conf` file in will need to be updated to include additional indexes *(see below)*.
-- The `datadir` option is now a part of `bitcoind` spawn configuration, and there is a new option to connect to multiple bitcoind processes (Please see [Bitcoin Service Docs](docs/services/bitcoind.md) for more details). The services `db` and `address` are now a part of the `bitcoind` service. Here is how to update `bitcore-node.json` configuration options:
+- The `datadir` option is now a part of `bitcoind` spawn configuration, and there is a new option to connect to multiple bitcoind processes (Please see [Bitcoin Service Docs](services/bitcoind.md) for more details). The services `db` and `address` are now a part of the `bitcoind` service. Here is how to update `bitcore-node.json` configuration options:
 
 **Before**:
 ```json