update chromedriver/geckodriver. closes SeleniumHQ#384

Merge branch 'master' of github.com:seleniumhq/docker-selenium

erbium release

update to dysprosium

push up major, major minor, major minor patch as well as latest

also push major and major.minor

first 3.0.1 release

Selenium 3.0 Dubnium

cerium release

berkelium release - use firefox 49 with geckodriver