add support for changing "w3c" option for Selenium2->ChromeDriver

[li0n12]

W3C WebDriver standart is enabled for ChromeDriver 75 by default.
We need to provide option to disable W3C support for services that don't support W3C standart.

it can be done with following config:

      default:
            extensions:
                Behat\MinkExtension:
                    sessions:
                        my_session:
                            selenium2: 
                                 chrome:
                                     w3c: false

[crossan007]

makes sense - this way you don't need to use extra_capabilities -> chromeOptions as in #345 (comment)