Bump Selenium version

Firefox 32 doesn't work with Webdriver 2.42 (at least on OSX Yosemite and maybe Mavericks): [#7810](https://code.google.com/p/selenium/issues/detail?id=7810) [#7823](https://code.google.com/p/selenium/issues/detail?id=7823).

Bumping to 2.43.1 fixed it, so the docs should maybe be updated.