fix(gen): Fixed missing `oauth` prop in `.yo-rc.json` after 2.0.5 update

Added proper update-process handling of `filters.oauth` property introduced [here](https://github.com/DaftMonk/generator-angular-fullstack/commit/316bd9dd3632622b0fb434cacfc4150f01d18e4c#diff-2018087f584c4398b5c3a23fc0e5f9dbR169).

Closes #403