Update Changelog for release of version 5.7.1

Author: LaunchDarklyCI

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 All notable changes to the LaunchDarkly Node.js SDK will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org).
 
+## [5.7.1] - 2019-01-16
+
+Changes are only in test code used by other libraries. There is no need to upgrade to this release.
+
 ## [5.7.0] - 2019-01-11
 ### Added:
 - It is now possible to inject feature flags into the client from local JSON or YAML files, replacing the normal LaunchDarkly connection. This would typically be for testing purposes. See `FileDataSource` in the [TypeScript API documentation](https://github.com/launchdarkly/node-client/blob/master/index.d.ts), and ["Reading flags from a file"](https://docs.launchdarkly.com/v2.0/docs/reading-flags-from-a-file).