buku: fix bukuserver (missing module)

[dermetfan]

Motivation for this change

bukuserver crashes on startup:

No module named 'flask_admin'

Traceback (most recent call last):
  File "/nix/store/5qi5nyzyj794d90jk4i91xbwnzc8p3qb-buku-4.2.2/bin/.bukuserver-wrapped", line 6, in <module>
    from bukuserver.server import cli
  File "/nix/store/5qi5nyzyj794d90jk4i91xbwnzc8p3qb-buku-4.2.2/lib/python3.7/site-packages/bukuserver/server.py", line 10, in <module>
    from flask_admin import Admin
ModuleNotFoundError: No module named 'flask_admin'

I just had to add the flask-admin package to the wrapper's PATH.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @matthiasbeyer @infinisil

[matthiasbeyer]

Diff looks good.

[teto]

I confirm the issue and this fixes it as well as passes nix-review.