Don't replace favicon if it isn't the default vue favicon

[AjBreidenbach]

Is your feature request related to a problem? Please describe.
In my case it followed a symlink to the parent project and overwrote the favicon there

Describe the solution you'd like
Check the favicon before writing

Describe alternatives you've considered
An alternative would be to add an option to the CLI to prevent this, or respect the option to not replace users files