QA: Update selenium-webdriver so Firefox 32 works

I did `bundle update`.
Without this, browser tests on Firefox 32 fail with
`unable to obtain stable firefox connection in 60 seconds
(127.0.0.1:7055) (Selenium::WebDriver::Error::WebDriverError)`

Change I26190cca06ee gave Flow the same update, this Gemfile.lock is
identical except Echo has a "chunky_png" gem.

Change-Id: I0b62134d38f3262b734af83cc58b644040857645