secret-handshake: fix broken link to source (#499)
secret-handshake: fix broken link to source (#499)


GKotfis/csharp,ErikSchierboom/xcsharp,exercism/xcsharp,robkeim/xcsharp,ErikSchierboom/xcsharp,GKotfis/csharp,exercism/xcsharp,robkeim/xcsharp