Add ability to pass ChromeOptions to the ChromeDriver.

I'm running tests in a Docker container
(https://hub.docker.com/r/gshakhn/sbt-firefox-chromium/).
Chrome and Docker don't play well together unless you pass
`--no-sandbox` to Chrome (elgalu/docker-selenium#9)
This change lets me set pass in `ChromeOptions` with the custom argument
to Chrome.

This is a breaking change since `Chrome` is now a class instead of an
object. Update readme to reflect that.

Other than the above, this should be backwards compatible.
The overloaded constructor of `ChromeDriver` just calls
`options.toCapabilities`, which has the old `DesiredCapabilities.chrome`
code.

Author: gshakhn

README.md

@@ -16,7 +16,7 @@ jsEnv := new org.scalajs.jsenv.selenium.SeleniumJSEnv(BROWSER)
 jsEnv in Test := new org.scalajs.jsenv.selenium.SeleniumJSEnv(BROWSER)
 ```
 where the `BROWSER` can be either `org.scalajs.jsenv.selenium.Firefox` or
-`org.scalajs.jsenv.selenium.Chrome`.
+`new org.scalajs.jsenv.selenium.Chrome`.
 
 When executing the program with `run` a new browser window will be created,
 the code will be executed in it and finally the browser will close itself.

seleniumJSEnv/src/main/scala/org/scalajs/jsenv/selenium/Chrome.scala

@@ -1,23 +1,23 @@
 package org.scalajs.jsenv.selenium
 
-import org.openqa.selenium.chrome.ChromeDriverService
+import org.openqa.selenium.chrome.{ChromeDriverService, ChromeOptions}
 import org.openqa.selenium.remote._
 
-object Chrome extends SeleniumBrowser {
+class Chrome(chromeOptions: ChromeOptions = new ChromeOptions) extends SeleniumBrowser {
+
   def name: String = "Chrome"
 
   def newDriver: BrowserDriver = new ChromeDriver
 
   private class ChromeDriver extends BrowserDriver {
     protected def newDriver(): RemoteWebDriver = {
-      val caps = DesiredCapabilities.chrome()
       val service = {
         /* Activate the silent ChromeDriverService silent mode,
          * see ChromeDriverService.createDefaultService
          */
         new ChromeDriverService.Builder().withSilent(true).usingAnyFreePort.build
       }
-      new org.openqa.selenium.chrome.ChromeDriver(service, caps)
+      new org.openqa.selenium.chrome.ChromeDriver(service, chromeOptions)
     }
   }
 }