git-bug: don't build unneeded packages, misc changes

* install fish completions
* meta.license update based on note in README

pkgs/applications/version-management/git-bug/default.nix

@@ -1,42 +1,43 @@
-{ lib, buildGoModule, fetchFromGitHub }:
+{ lib, buildGoModule, fetchFromGitHub, installShellFiles }:
 
 buildGoModule rec {
   pname = "git-bug";
-  version = "0.8.0"; # the `rev` below pins the version of the source to get
-  rev = "v0.8.0";
+  version = "0.8.0";
 
   src = fetchFromGitHub {
-    inherit rev;
     owner = "MichaelMure";
     repo = "git-bug";
+    rev = "v${version}";
     sha256 = "12byf6nsamwz0ssigan1z299s01cyh8bhgj86bibl90agd4zs9n8";
   };
 
   vendorSha256 = "sha256-32kNDoBE50Jx1Ef9YwhDk7nd3CaTSnHPlu7PgWPUGfE=";
 
+  nativeBuildInputs = [ installShellFiles ];
+
   doCheck = false;
 
+  excludedPackages = [ "doc" "misc" ];
+
   ldflags = [
-    "-X github.com/MichaelMure/git-bug/commands.GitCommit=${rev}"
+    "-X github.com/MichaelMure/git-bug/commands.GitCommit=v${version}"
     "-X github.com/MichaelMure/git-bug/commands.GitLastTag=${version}"
     "-X github.com/MichaelMure/git-bug/commands.GitExactTag=${version}"
   ];
 
   postInstall = ''
-    install -D -m 0644 misc/completion/bash/git-bug "$out/share/bash-completion/completions/git-bug"
-    install -D -m 0644 misc/completion/zsh/git-bug "$out/share/zsh/site-functions/git-bug"
-    install -D -m 0644 -t "$out/share/man/man1" doc/man/*
+    installShellCompletion \
+      --bash misc/completion/bash/git-bug \
+      --zsh misc/completion/zsh/git-bug \
+      --fish misc/completion/fish/git-bug
 
-    # not sure why the following executables are in $out/bin/
-    rm -f $out/bin/cmd
-    rm -f $out/bin/completion
-    rm -f $out/bin/doc
+    installManPage doc/man/*
   '';
 
   meta = with lib; {
     description = "Distributed bug tracker embedded in Git";
     homepage = "https://github.com/MichaelMure/git-bug";
-    license = licenses.gpl3Only;
-    maintainers = with maintainers; [ royneary ];
+    license = licenses.gpl3Plus;
+    maintainers = with maintainers; [ royneary DeeUnderscore ];
   };
 }