fix new files in Safari

fixes: CNVS-15200

freaking Safari doesn't implement the URLUtils
interface so we can't use `new URL`
see: https://developer.mozilla.org/en-US/docs/Web/API/URL

test plan:
* open new files in safari
  (and FF, IE, & chrome to be thorough)
* it should load.

Change-Id: Ieb219bd019e029020a572580987c98d2c93c1014
Reviewed-on: https://gerrit.instructure.com/40319
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>