Acceptance test Error: ReferenceError: Can't find variable: Set

We've encountered this in many situations (e.g. Ben and Sam's laptops) - seems to be usage of an ES6 idiom (Set?) that our javascript driver cannot cope with. Has been solved in the past with upgrading to phantomjs-beta

```
1) test when a user chooses 'mob' from the homepage, they are added to a single shared Jitsi (Paironauts.AcceptanceTest)
test/browser/acceptance_test.exs:21
** (Wallaby.JSError) There was an uncaught javascript error:

ReferenceError: Can't find variable: Set
e (https://www.jitsi.agileventures.org/libs/lib-jitsi-meet.min.js?v=2917:2)
(anonymous function) (https://www.jitsi.agileventures.org/libs/lib-jitsi-meet.min.js?v=2917:2)
(anonymous function) (https://www.jitsi.agileventures.org/libs/lib-jitsi-meet.min.js?v=2917:2)
t (https://www.jitsi.agileventures.org/libs/lib-jitsi-meet.min.js?v=2917:2)
```

Paironauts codebase includes some javascript in e.g. assets/js that will run in the javascript driver. As part of our app we also embed jitsi's, and so some of our templates pull in js code from places like: https://meet.jit.si/external_api.js and then on top of that it will add other javascript file requirements when the jitsi itself is embedded in `