Run npm run build to generate resources.json during packaging time

[ShivanKaul]

We currently consume resources.json (https://github.com/brave/adblock-resources/blob/master/dist/resources.json) in crx-packager. This requires remembering to run npm run build when adding/editing a resource under resources/ like in brave/adblock-resources#207

We should just run npm run build in crx-packager on the raw resources.

[ryanbr]

My npm build in LTS is 8, which isn't supported :(

[antonok-edm]

@ryanbr what @ShivanKaul is saying is we can run it on the servers, so you won't need any extra steps