Fix client-side onerror handling no working due to missing crossorigin attribute for CDN scripts

[wentsul]

Couple things to note:

• This needs to be set for __webpack_public_path__ but not sure if it should always be set for "critical chunk" scripts.
• I this fork deployed for a production and I'm now seeing client-side errors. Previously I was seeing "Script error." line 0.
• More information on why here: https://blog.sentry.io/2016/05/17/what-is-script-error
• Would to keep the tests but wasn't sure how to update the tests to only check for critical scripts. Changing el.crossOrigin === 'anonymous' was failing so I'm assuming there are other scripts.