Fix link formatting in the Clock exercise's README (#753)
Fix link formatting in the Clock exercise's README (#753)

* Fix link formatting in the Clock exercise's README

* Update exercises/clock/README.md

Directly link to .NET Core 2.1

Co-Authored-By: vamcs <8ea8feea523aa0407d2e670f1c32a9dea7d2aacf@gmail.com>

robkeim/xcsharp,robkeim/xcsharp,exercism/xcsharp,ErikSchierboom/xcsharp,exercism/xcsharp,ErikSchierboom/xcsharp