Use a timeout when calling RequestShutdown()

Author: yannickcholette

src/Client/LanguageClient.cs

@@ -423,7 +423,16 @@ public async Task Shutdown()
         {
             if (_connection.IsOpen)
             {
-                await this.RequestShutdown().ConfigureAwait(false);
+                try
+                {
+                    // this can get stuck forever, so use a timeout.
+                    var cancelSource = new CancellationTokenSource();
+                    cancelSource.CancelAfter(5 * 1000);
+
+                    await this.RequestShutdown(cancelSource.Token).ConfigureAwait(false);
+                }
+                catch (TaskCanceledException) { }
+
                 this.SendExit();
             }