Merge pull request #1522 from github/fixes/1520-VS2017-deadlock

Call MenuCommandService.AddCommand on Main thread

Author: jcansdale

src/GitHub.VisualStudio/GitHubPackage.cs

@@ -7,6 +7,7 @@
 using System.Windows;
 using GitHub.Api;
 using GitHub.Extensions;
+using GitHub.Helpers;
 using GitHub.Info;
 using GitHub.Logging;
 using GitHub.Models;
@@ -76,6 +77,9 @@ async Task InitializeMenus()
                 return;
             }
 
+            // IMenuCommandService.AddCommand uses IServiceProvider.GetService and must be called on Main thread.
+            await ThreadingHelper.SwitchToMainThreadAsync();
+
             foreach (var menu in menus.Menus)
                 serviceProvider.AddCommandHandler(menu.Guid, menu.CmdId, (s, e) => menu.Activate());