Allow BaseUris without scheme.

We now allow the enterprise URL to be entered without a scheme, but `new Uri(string)` requires a scheme. Use `new UriBuilder(string).Uri` instead which assumes http.

Author: grokys

src/GitHub.App/ViewModels/Dialog/LoginToGitHubForEnterpriseViewModel.cs

@@ -113,7 +113,7 @@ public EnterpriseLoginMethods? SupportedLoginMethods
 
         public ReactivePropertyValidator EnterpriseUrlValidator { get; }
 
-        protected override Uri BaseUri => new Uri(EnterpriseUrl);
+        protected override Uri BaseUri => new UriBuilder(EnterpriseUrl).Uri;
 
         public IReactiveCommand<Unit> NavigateLearnMore
         {