Update Miniflux Version
Hey
I was experimenting with running through the getting started steps on my Raspberry Pi.
Since, the version being used at the moment does not provide arm images, the getting started guide fails at the miniflux setup. If we update it to the latest version miniflux/miniflux:2.0.21
we can solve this issue as it provides an arm image.
If this sounds fine, I can send a PR to update the version.