alembic: 1.7.6 -> 1.7.7

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/alembic/versions.

These checks were done:

- built on NixOS
- ran `/nix/store/739vhfkmanak88f4g6yzqkrsid2mi59r-alembic-1.7.7-bin/bin/abcls -h` got 0 exit code
- ran `/nix/store/739vhfkmanak88f4g6yzqkrsid2mi59r-alembic-1.7.7-bin/bin/abcls --help` got 0 exit code
- ran `/nix/store/739vhfkmanak88f4g6yzqkrsid2mi59r-alembic-1.7.7-bin/bin/abcls help` got 0 exit code
- ran `/nix/store/739vhfkmanak88f4g6yzqkrsid2mi59r-alembic-1.7.7-bin/bin/abctree -h` got 0 exit code
- ran `/nix/store/739vhfkmanak88f4g6yzqkrsid2mi59r-alembic-1.7.7-bin/bin/abctree --help` got 0 exit code
- ran `/nix/store/739vhfkmanak88f4g6yzqkrsid2mi59r-alembic-1.7.7-bin/bin/abcconvert --help` got 0 exit code
- found 1.7.7 with grep in /nix/store/739vhfkmanak88f4g6yzqkrsid2mi59r-alembic-1.7.7-bin
- directory tree listing: https://gist.github.com/ef5ac862933e11b24f7c82cf0d0c4b16