Update the Strava provider to use the non-standard comma-separated scopes format

Author: anderaus

src/AspNet.Security.OAuth.Strava/StravaAuthenticationHandler.cs

@@ -58,5 +58,7 @@ protected override async Task<AuthenticationTicket> CreateTicketAsync([NotNull]
 
             return context.Ticket;
         }
+
+        protected override string FormatScope() => string.Join(",", Options.Scope);
     }
 }