After making `ffmpeg` point to the latest `ffmpeg_4`, all packages that
used `ffmpeg` without requiring a specific version now use ffmpeg_3
explicitly so they shouldn't change.
According to https://repology.org/repository/nix_unstable/problems, we have a
lot of packages that have http links that redirect to https as their homepage.
This commit updates all these packages to use the https links as their
homepage.
The following script was used to make these updates:
```
curl https://repology.org/api/v1/repository/nix_unstable/problems \
| jq '.[] | .problem' -r \
| rg 'Homepage link "(.+)" is a permanent redirect to "(.+)" and should be updated' --replace 's@$1@$2@' \
| sort | uniq > script.sed
find -name '*.nix' | xargs -P4 -- sed -f script.sed -i
```
