[mod] filtron.sh - install github.com/searxng/filtron

SearXNG maintains a fork of filtron at [1]

[1] https://github.com/searxng/filtron

Related: https://github.com/searxng/searxng/issues/507#issuecomment-970254027


Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>