keep minimum strip count

[cfinck27]

Potential fix for #153

Since these are all old strips that aren't being updated, they are never more recent than expirationDate, which means only the first strip is kept:

.filter((strip, i) => (i === 0 || new Date(strip.date) > expirationDate)) // keeps recent strips

To mitigate this I added a minimumCount variable that applies globally, but this could also be moved to a per-scraper value.

Not sure what the other options are since these aren't being updated, but if there's still a desire to see some in the feed then this is probably the best compromise.

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https://github.com/ArtskydJ/comicsrss.com/blob/8aecc970c5f7834d353f187b1068cb50a4223dbb/_generator/bin.js#L128-L134