Kolibri: Syntax error in IE11 on builds from 'develop' branch

[radinamatic]

Observed behavior

Syntax error impeding develop Kolibri to load in IE11.

Errors and screenshot

Expected behavior

We still need to support IE11, so need to cater to its _idiosyntaxies_ 🤷🏽‍♀️

Context

• Kolibri version: exe asset built from the develop branch
• Operating system: Windows 7
• Browser: IE11

cc @rtibbles

[rtibbles]

This is almost certainly a regression from the babel upgrade. Will fix.

[rtibbles]

Looks like the specific syntax error is being caused by an untranspiled class definition.

[rtibbles]

There are two issues here, seemingly - one is that fuse.js by default exports a non-transpiled ES Module, which was being imported but not transpiled. The other is that our new core-js configuration was incorrect, so Object.assign and other vital polyfills were not being imported.