fix: Fix ChromeHeadless in Docker (shaka-project#51)

Currently ChromeHeadless cannot be run in the Docker environment due to
lack of `--no-sandbox` argument. Trying to run ChromeHeadless within
Docker ends with `DevToolsActivePort file doesn't exist` error. You can
find more info here:
https://bugs.chromium.org/p/chromedriver/issues/detail?id=2473

Of course this can be omitted by creating custom launcher, but I
believe this can be so common issue it's better to tackle it by default.
Additionally I'm planning to add running tests within Docker to shaka,
so it'll easify process.

index.js

@@ -279,6 +279,7 @@ const LocalWebDriverChromeHeadless = generateSubclass(
       'goog:chromeOptions': {
         args: [
           '--headless',
+          '--no-sandbox',
           '--disable-gpu',
           '--disable-dev-shm-usage',
         ],