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.
In line with the Nixpkgs manual.
A mechanical change, done with this command:
find pkgs -name "*.nix" | \
while read f; do \
sed -e 's/description\s*=\s*"\([a-z]\)/description = "\u\1/' -i "$f"; \
done
I manually skipped some:
* Descriptions starting with an abbreviation, a user name or package name
* Frequently generated expressions (haskell-packages.nix)
