When using Google auth for admin, always prompt for which account.

This makes it a bit easier to switch between accounts if you have
multiple, but happen to only be signed into 1.

src/api-umbrella/web-app/config/initializers/devise.rb

@@ -287,6 +287,7 @@
       config.omniauth :google_oauth2,
         ApiUmbrellaConfig[:web][:admin][:auth_strategies][:google][:client_id],
         ApiUmbrellaConfig[:web][:admin][:auth_strategies][:google][:client_secret],
+        :prompt => "select_account",
         :scope => "userinfo.email"
     when "ldap"
       require "omniauth-ldap"