Bug report

When pushing new content to a VuePress site with the themeConfig.serviceWorker.updatePopup enabled the popup only shows up the first page reload - if you don't click the refresh button the popup no longer appears for subsequent page reloads.

Version

VuePress 0.13.0

Steps to reproduce

1. Create a new commit
2. Refresh the page to see the new content popup
3. Refresh the page again and the new content popup doesn't appear

What is expected?

The service worker update popup should appear as long as there is a new service worker available.

What is actually happening?

The service worker update popup appears on refresh with new content but doesn't appear again if you refresh without clicking the update button.

Other relevant information

Your OS: macOS High Sierra v10.13.6
Node.js version: v9.1.0
Browser version: Version 68.0.3440.75 (Official Build) (64-bit)
Is this a global or local install? Global
Which package manager did you use for the install? Yarn