Update docs for wallabyTest.ts

[mwymann]

I had an issue starting wallaby:
Uncaught ReferenceError: Zone is not defined

After hours of research I found the solution coincidentally.
The imports in wallabyTest.ts are dependent on each other, so order really matters.
import './polyfills';
import 'core-js/es7/reflect';
import 'zone.js/dist/zone-testing';
// imports of angular testing modules...

Unfortunately I had a personal setting in VS Code:
"editor.codeActionsOnSave": {
"source.organizeImports": true
}
So everytime I saved the file the order of imports changed and wallaby crashed.

Maybe you could update your docs with a hint on this... ;-)

[ArtemGovorov]

Thanks for the note! I'd also report the issue to VS Code team as it doesn't seem to be a correct behaviour to change the order of the imports where the order matters.