Chromedriver-helper overrides chromedriver path

[Maros Hluska]

Installing this gem seems to break my selenium tests because the gem chromedriver-helper overrides the chromedriver binary path. It would be useful to be able to provide my own chromedriver path via environment variable.

[Maxim Ivanov]

Just a dev note here, need to add binary: '/path/to/binary' (parameterize this) to options constructor as per http://seleniumhq.github.io/selenium/docs/api/rb/Selenium/WebDriver/Chrome/Options.html

This would likely be set in the configs rather than an env variable, the config itself can use erb though to read env vars