Don't cache service-worker.js when using pwa plugin

[Narkoleptika]

Hello, thanks for this and the apollo plugins! Just a real quick change here.

I'm using this plugin along with the pwa plugin and am receiving the following warning on Chrome 69.0.3497.92

The last argument to serve needs to either be omitted or changed to false on the following line: https://github.com/Akryum/vue-cli-plugin-ssr/blob/master/lib/app.js#L80

Thanks!

[mrksbnch]

@Akryum As this should probably be fixed and is an easy change (https://github.com/Akryum/vue-cli-plugin-ssr/blob/master/lib/app.js#L83), would you accept a MR for this?

[Akryum]

Of course! :)