Service worker does not invalidate bundle

[karatechops]

The current offline plugin does not invalidate site bundles when a new bundle is available. To see new versions of the site I have to perform a hard refresh in my browser. For instance, I was still seeing #67 until I shift + refreshed.

[crashuniverse]

@karatechops Would it be relevant to mention that service workers close when all instances stop and loads the new bundle next time you reach the page? I'll give this a try myself (I haven't yet) but thought to throw this question to see what you think about what happened.