Increase Capybara timeout for rspec

The default 60 seconds fails somewhat regularly. While making our Middleman setup faster would be nice, it's not really in scope for these specs.

(In !16980 (merged), I let the rspec job fail. This should stop it failing, but what I really want is 'allowed to fail on master'. At present, if this is not allowed to fail, then failures will block master deploys.)