plantuml-server: fixed unstable deps
plantuml-server: fixed unstable deps

after merging https://github.com/NixOS/nixpkgs/pull/163431 `plantuml-server-*-deps` derivation turned out unstable, this commit switches to fetching `plantuml.war` directly from releases

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs