syntax highlighting broken in yaml as of build ST4142

[DavidHe1127]

The issue was seen and reported. And I'm not sure if a change needs to be made to fix it in ayu packages - see this. Therefore, I created this issue for you guys to have a further look and confirm.

[danielskowronski]

Sublime team probably won't fix that soon - sublimehq/Packages#3288 is still open...

It's a matter of adding a new rule to colour scheme, for example in Ayu Dark assuming keys should be coloured as keywords:

{
  "name": "Mapping Key Names",
  "scope": "meta.property-name,meta.mapping.key string.quoted.double, meta.mapping.key string",
  "foreground": "#ff8f40"
}

Updated scope to catch JSON as well.