Update CHANGELOG for v1.7.0

***NO_CI***

Author: nfbot

CHANGELOG.md

@@ -2,7 +2,15 @@
 
 ## [**Changes available only in 'Preview' NuGet packages:**](https://github.com/nanoframework/System.Net/tree/HEAD)
 
-[Full Changelog](https://github.com/nanoframework/System.Net/compare/v1.7.0-preview.4...HEAD)
+[Full Changelog](https://github.com/nanoframework/System.Net/compare/v1.7.0-preview.6...HEAD)
+
+**Documentation and other chores:**
+
+- Update 2 nuget dependencies [\#198](https://github.com/nanoframework/System.Net/pull/198)
+
+## [v1.7.0-preview.6](https://github.com/nanoframework/System.Net/tree/v1.7.0-preview.6) (2021-07-14)
+
+[Full Changelog](https://github.com/nanoframework/System.Net/compare/v1.7.0-preview.4...v1.7.0-preview.6)
 
 **Documentation and other chores:**