allow insecure SSL with behat, mink, selenium

this was annoying and hard to find on the internet, so here it is

extensions:
    Behat\MinkExtension:
      selenium2:
        browser: chrome
        wd_host: "http://127.0.0.1:4444/wd/hub"
        capabilities: {"extra_capabilities": {"acceptInsecureCerts": true}}