Use absolute worker path to fix document loading in packaged apps

[navhaxs]

Issue:
In the packaged release apps there is currently a problem with loading a document - the service worker is failing to initialise:
#48
#36

Analaysis:
In the packaged Electron app the relative path './src/service/worker.js' no longer works. See https://stackoverflow.com/a/71098112

Fix:
The solution is to use the correct absolute path by using __dirname.

Testing:
I have tested and verified this fix with npm run package on macOS .

(Could someone verify this fix for Windows and Linux packaged apps too?)