maintainers/scripts/haskell: briefer commit message bodies

The “This commit was generated by …” message is very wordy and often
exceeds 72 characters which is a good (loose) target for wrapping lines
in commit messages.

maintainers/scripts/haskell/update-hackage.sh

@@ -54,7 +54,7 @@ git add pkgs/data/misc/hackage/pin.json
 git commit -F - << EOF
 all-cabal-hashes: $version_diff
 
-This commit has been generated by maintainers/scripts/haskell/update-hackage.sh
+(generated by maintainers/scripts/haskell/update-hackage.sh)
 EOF
 else
 echo "$version_diff"