App could not auto update

[Anduin2017]

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Environment

• Environment: Production
• Last git commit: 1817520
• Platform: PWA
• Browser: Chrome

How to repro

• Step 1: Pin 3.1.0 to the home screen.
• Step 2: Wait for 3.1.1 release.
• Step 3: Try refreshing.

And then the app was not upgraded and still 3.1.0. No matter how many times I refresh. I even tried uninstalling the Kahla PWA app and reinstall it. Still 3.1.0

Expected situation

I expect that the app could be upgraded to 3.1.1.

Other information

Is there something wrong with our service worker?

[xxyzz]

I think we should add cache-control and expires headers to the kahla.app server. Although the service worker tries to fetch after using the cached files, it gets them from the browser disk cache.