Pull request to wait for Twitter & Google Plus

This pull request lengthens a test timeout, tightly targeting the 'invitation thank you' modal window, helping ensure it loads completely (especially on constrained developer systems).

This not only increases the robustness of the current tests, but also gives elbow room to add more social app buttons in future.

This source change flows into gem rails_apps_composer [here](https://github.com/RailsApps/rails_apps_composer/blob/master/recipes/prelaunch.rb#L102).